Question

bai1:CMR

a, (a-1).(a-2)+(a-3).(a+4)-(2a^2+5a-34)=-7a+24

b,(a+c)(a-c)-b(2a-b)-(a-b+c).(a-b-c)=0

 

Answer 1

b. \(\left(a+c\right)\left(a-c\right)-b\left(2a-b\right)-\left(a-b+c\right)\left(a-b-c\right)\)

=\(\left(a^2-c^2\right)-2ab+b^2-\left(a-b\right)^2+c^2\)

=\(a^2-c^2-2ab+b^2-a^2+2ab-b^2+c^2\)

=0=VP=> đpcm

Answer 2

a. \(\left(a-1\right)\left(a-2\right)+\left(a-3\right)\left(a+4\right)-\left(2a^2+5a-34\right)\)

=\(\left(a^2-3a+2\right)+\left(a^2+a-12\right)-\left(2a^2+5a-34\right)\)

=\(a^2-3a+2+a^2+a-12-2a^2-5a+34\)

=-7a+24

=VP => đpcm