Functions

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Functions

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UNIT 2: FUNCTIONS

Practice questions covering lines, quadratics, domain and range, composite functions, inverse functions, transformations, perpendicular bisector, asymptotes, exponential and logistic models, sinusoidal models, piecewise functions, curve sketching, and more.

Q1 [EASY]

Find the gradient and y-intercept of the line 3x − 2y + 6 = 0.

Answer: Gradient = 3/2; y-intercept = (0, 3)

Q2 [EASY]

Line L passes through (2, −1) and (6, 7). Find the equation of L in the form y = mx + c.

Answer: m = (7−(−1))/(6−2) = 2; y−(−1) = 2(x−2) → y = 2x − 5

Q3 [EASY]

Given f(x) = 3x² − 2x + 1. Find: (a) f(0), (b) f(−2), (c) the axis of symmetry.

Answer: (a) 1 (b) 17 (c) x = 1/3

Q4 [EASY]

State the domain and range of f(x) = √(x − 3).

Answer: Domain: x ≥ 3 (i.e. [3,+∞)); Range: y ≥ 0 (i.e. [0,+∞))

Q5 [EASY]

Given f(x) = 2x + 1 and g(x) = x². Find (a) f∘g(x), (b) g∘f(x), (c) f∘g(3).

Answer: (a) 2x²+1 (b) (2x+1)² (c) 19

Q6 [EASY]

Find the inverse of f(x) = 4x − 7. State its domain and range.

Answer: f⁻¹(x) = (x+7)/4; Domain and range: all real numbers

Q7 [EASY]

Describe the transformations that map f(x) = x² onto g(x) = −(x+3)² + 5.

Answer: Translate left 3, reflect in x-axis, translate up 5

Q8 [MEDIUM]

Line L₁ has equation 2x + 3y = 12. Line L₂ is perpendicular to L₁ and passes through (4, 1).

(a) Find the gradient of L₁.

(b) Write the equation of L₂.

(c) Find the intersection of L₁ and L₂.

Answer: (a) m₁=−2/3 (b) y=1.5x−5 (c) (126/13, 3/13)

Q9 [MEDIUM]

Find the perpendicular bisector of the segment joining A(1, 4) and B(7, −2). Write in the form ax + by = c.

Answer: Midpoint (4,1), slope=1, equation: x − y = 3

Q10 [MEDIUM]

Consider f(x) = (x−2)/(x+1).

(a) State the domain.

(b) Find f⁻¹(x).

(c) State the domain of f⁻¹.

(d) Find the equations of the asymptotes of f.

Answer: (a) x∈ℝ, x≠−1 (b) f⁻¹(x)=−(x+2)/(x−1) (c) x≠1 (d) x=−1, y=1

Q11 [MEDIUM]

The exponential model P(t) = 1200·e^(0.03t) represents a population after t years.

(a) Find P(0).

(b) Find the population after 10 years.

(c) Find when P = 3600 (give t to 1 d.p.).

(d) State the meaning of 0.03 in context.

Answer: (a) 1200 (b) ≈1619 (c) t≈36.6 years (d) 3% per year continuous growth rate

Q12 [MEDIUM]

f(x) = 3sin(2x − π/4) − 1. Find: (a) amplitude, (b) period, (c) principal axis, (d) phase shift, (e) maximum and minimum values.

Answer: (a) 3 (b) π (c) y=−1 (d) π/8 right (e) Max=2, Min=−4

Q13 [MEDIUM]

Use your GDC to solve 2x³ − 5x + 1 = 0, giving all solutions to 3 s.f.

Answer: x ≈ −1.66, x ≈ 0.201, x ≈ 1.46

Q14 [MEDIUM]

f(x) = ln(2x−3).

(a) State the domain and range.

(b) Sketch the graph, showing the x-intercept and vertical asymptote.

(c) Find f⁻¹(x) and state its domain.

Answer: (a) x>3/2, y∈ℝ (b) x-int=(2,0), VA: x=1.5 (c) f⁻¹(x)=(eˣ+3)/2

Q15 [MEDIUM]

The graph of f(x) is transformed to g(x) = 2f(3x−6) + 4.

(a) Describe each transformation in the correct order.

(b) If f(x) has domain [0,6] and range [−2,4], find the domain and range of g.

Answer: (a) Horizontal compression ×1/3, right 2; vertical stretch ×2, up 4 (b) Domain [2,4], Range [0,12]

Q16 [MEDIUM]

The logistic function is P(t) = 500/(1 + 4e^(−0.2t)).

(a) Find P(0).

(b) Find the carrying capacity (horizontal asymptote as t→∞).

(c) Find t when P=450 to 1 d.p.

(d) State the point of inflection.

Answer: (a) 100 (b) 500 (c) t≈17.9 (d) At P=250, t≈6.93

Q17 [MEDIUM]

Points A(1,3), B(5,7), C(8,2) form a triangle. Find:

(a) the equation of the altitude from A to BC,

(b) the centroid,

(c) the circumcentre.

Answer: (a) y=(3/5)x+12/5 (b) Centroid=(14/3, 4) (c) Circumcentre≈(4.5, 4.1)

Q18 [HARD]

f(x) = ln(x) + 2 and its inverse f⁻¹(x) = e^(x−2).

(a) Verify algebraically that f and f⁻¹ are inverse functions.

(b) Find the point(s) where f(x) = f⁻¹(x) and where both cross y=x.

(c) Find (f∘f⁻¹)(e) and (f⁻¹∘f)(4).

(d) Solve f(f(x)) = 3, giving answer to 3 d.p.

Answer: (a) Verified (b) Solve numerically via GDC (c) e and 4 (d) x≈5.575

Q19 [HARD]

g(x) = 3sin(2x − π/3) + 1 and original f(x) = sin(x).

(a) Show the transformations step by step from f to g.

(b) State the range of g and find all x ∈ [0, 2π] where g(x) = 0.

(c) Find the area enclosed between g(x) and y=1 over one full period.

(d) [HL] Find all x ∈ ℝ where g(x) = f(x), i.e. 3sin(2x−π/3)+1 = sin(x).

Answer: (a) Shown (b) Range [−2,4]; zeros at x≈0.71,1.34,3.85,4.48 (approx) (c) 6 (d) Via GDC

Q20 [HARD]

Piecewise function: for x<0: f(x)=x²+1; for 0≤x≤2: f(x)=−2x+4; for x>2: f(x)=2^(x−2)−1.

(a) Show f is NOT continuous at x=0.

(b) Find any zeros of f.

(c) Find the domain and range.

(d) Find f⁻¹(x) for the linear piece, and state its domain.

(e) Evaluate ∫₀² f(x) dx.

Answer: (a) Shown (lim=1≠f(0)=4) (b) x=2 (c) Domain ℝ, Range (−1,∞) (d) f⁻¹(x)=(4−x)/2, x∈[0,4] (e) 4

Q21 [HARD]

f(x) = (2x+a)/(bx+3) has a vertical asymptote at x=1 and passes through (0,2) and (2,5).

(a) Use the asymptote to find b.

(b) Use (0,2) to find a.

(c) Verify with point (2,5).

(d) Find f⁻¹(x) and state its domain.

(e) Find all x where f(x) = f⁻¹(x).

Answer: (a) b=−3 (b) a=6 (c) Verify with GDC (d) f⁻¹(x)=(3−3x)/(3x+2) (e) x=1±√(7/3) via GDC

Q22 [HARD]

Sinusoidal model: temperature T(t) = a·cos(bt) + d. Max 34°C at 2pm (t=14), min 18°C at 2am (t=2).

(a) Find a, d, b, and the period.

(b) Write the full equation T(t).

(c) Find the times when T = 28°C during one day.

(d) Find the average temperature over a 24-hour period.

Answer: (a) a=8, d=26, b=π/12, period=24h (b) T(t)=8cos(π(t−14)/12)+26 (c) t≈8.9h and t≈19.1h (d) 26°C

Q23 [HARD] [HL]

Let f(x) = e^x and g(x) = 3x².

(a) Find all solutions to f(x) = g(x) to 3 s.f.

(b) For the smallest positive solution, find the angle between the two curves.

(c) Find the area enclosed between f and g for x ∈ [−1, 0].

(d) Show (f∘g)(x) = e^(3x²) and find its minimum value and the x-values where it occurs.

Answer: (