Question

Tính :

( 2a + b - 5 ) x ( 2a - b + 5 )

Answer 1

\(\left(2a+b-5\right)\left(2a-b+5\right)=\left[2a+\left(b-5\right)\right]\left[2a-\left(b-5\right)\right]=4a^2-\left(b-5\right)^2hoặc\left(2a+b-5\right)\left(2a-b+5\right)=4a^2-2ab+10a+2ab-b^2+5b-10a+5b-25=4a^2-b^2+10b-25=4a^2-\left(b-5\right)^2\)

Answer 2

(2a+b-5).(2a-b+5)

=2a(2a-b+5)+b(2a-b+5)-5(2a-b+5)

=4a\(^2\) -2ab+10a+2ab-b\(^2\)+5b-10a+5b-25

=4a\(^{2^{ }}\)-25-b\(^2\)