please help

Question

Simplify

Multiply

(2�ã7-4�ã2)(5�ã7+10�ã2)

Answer 1

Assuming your garbled symbol means √, we have

(2√7 - 4√2)(5√7 + 10√2)
just think of these as polynomials in x and y

(2x-4y)(5x+10y) = 10x^2 - 40y^2

letting x = √7 and y = √2, we have

10(√7)^2 - 40(√2)^2 = 10*7-40*2 = -10

Some work could have been saved by noting that

(2√7 - 4√2)(5√7 + 10√2)
= 2(√7-2√2) * 5(√7+√2)
= 10(√7-2√2)(√7+2√2)
= 10(7-8)