If f:R→Rf: \mathbb{R} \to \mathbb{R} is defined as f(x)=x2−3x+2f(x) = x^2 - 3x + 2, find f(f(x))f(f(x)).

Answer: f(f(x)) = x4−6x3+10x2−3xx^4 - 6x^3 + 10x^2 - 3x

Step-by-step solution

Step 1: Set up the composite function

To evaluate the composite function f(f(x))f(f(x)), replace every occurrence of the input variable xx in f(x)=x2−3x+2f(x) = x^2 - 3x + 2 with the expression for f(x)f(x) itself, which is x2−3x+2x^2 - 3x + 2.

Step 2: Expand the squared trinomial

Apply the identity (a+b+c)2=a2+b2+c2+2ab+2bc+2ca(a + b + c)^2 = a^2 + b^2 + c^2 + 2ab + 2bc + 2ca with a=x2a = x^2, b=−3xb = -3x, and c=2c = 2. Combining the like terms gives x4−6x3+13x2−12x+4x^4 - 6x^3 + 13x^2 - 12x + 4.

Step 3: Expand the linear term and constant

Distribute the factor of −3-3 across the terms inside (x2−3x+2)(x^2 - 3x + 2) to get −3x2+9x−6-3x^2 + 9x - 6, and then add the constant +2+2, which simplifies to −3x2+9x−4-3x^2 + 9x - 4.

Step 4: Combine all terms to find final expression

Add the two expanded parts together by combining like powers of xx: x4x^4 remains as is; −6x3-6x^3 remains as is; for the degree 2 term, 13x2−3x2=10x213x^2 - 3x^2 = 10x^2; for the degree 1 term, −12x+9x=−3x-12x + 9x = -3x; and for the constants, 4−4=04 - 4 = 0.

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