Answer:
A) -84x^3 - 8x
B) -91x^4 + 143x^2 - 65x
C) 12b^2 - 7b - 10.
D) 16x^2 - 72x + 81
Explanation:
A) -4x(21x^2-3x+2)
B) -13x(7x^3-11x+5)
C) (3b+2)(4b-5)
D) (4x-9)^2
In A) -4x(21x^2-3x+2) we are multiplying the binomial (21x^2-3x+2) by the monomial -4x; there are two multiplications involved:
-4x(21x^2) = -84x^3
and
-4x(-3x+2) = +12x^2 - 8x.
Hence A) -4x(21x^2-3x+2) = -84x^3 - 8x
B) The work done to find the product in B) is similar: Multiply each term in 7x^3-11x+5 by -13x:
The end result is -91x^4 + 143x^2 - 65x
C) Here we are multiplying together two binomials; we use the FOIL method: Multiply together the First terms, then the Outer terms, then the Inner terms, and finally the Last terms. This results in:
(3b+2)(4b-5) = 12b^2 -15b + 8b -10, or, after simplification, 12b^2 - 7b - 10.
In D) we are squaring a binomial. The formula for this is:
(a - b)^2 = a^2 - 2ab + b^2. Here,
(4x - 9)^2 = 16x^2 - 2(36x) + 81, or 16x^2 - 72x + 81