?
A = $$\frac{{{x^8} - 1}}{{{x^4} + 1}}$$ and B = $$\frac{{{y^4} - 1}}{{{y^2} + 1}}.$$ If x = 2 and y = 9, then what is the value of A2 + 2AB + AB2?
Answer & Solution
Correct Answer:
Option
B
$$\eqalign{
& A = \frac{{{x^8} - 1}}{{{x^4} + 1}} = \frac{{\left( {{x^4} + 1} \right)\left( {{x^4} - 1} \right)}}{{\left( {{x^4} + 1} \right)}} = {x^4} - 1 \cr
& B = \frac{{{y^4} - 1}}{{{y^2} + 1}} = \frac{{\left( {{y^2} + 1} \right)\left( {{y^2} - 1} \right)}}{{\left( {{y^2} + 1} \right)}} = {y^2} - 1 \cr
& x = 2,\,\,y = 9 \cr
& A = {x^4} - 1 = {\left( 2 \right)^4} - 1 = 15 \cr
& B = {y^2} - 1 = {\left( 9 \right)^2} - 1 = 80 \cr
& {A^2} + 2AB + A{B^2} \cr
& = {\left( {15} \right)^2} + 2 \times 15 \times 80 + 15 \times {\left( {80} \right)^2} \cr
& = 15\left( {15 + 160 + 6400} \right) \cr
& = 15 \times \left( {6575} \right) \cr
& = 98625 \cr} $$
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