Question

①x2-8x-7=0②x2+14x-15=0③t2-(2/3)t-(8/9)=0④4(x+3)2-9(x-2)2=0

Answer 1

①x2-8x-7=0

Δ=64+4×7=64+28=92;

x=(8±2√23)/2=4±√23;

(②x2+14x-15=0

(x+15)(x-1)=0;

x=1或x=-15；

③t2-(2/3)t-(8/9)=0

(t-4/3)(t+2/3)=0;

t=4/3或t=-2/3;

④4(x+3)2-9(x-2)2=0

4(x+3)²=9(x-2)²;

2(x+3)=±3(x-2);

2x+6=3x-2或2x+6=-3x+2；

x=8或x=-4/5;