Đáp án:
Giải thích các bước giải:
7. x4- 5x²+ 4= x4- x²- 4x²+ 4= x². (x²-1)-4. (x²-1)
= (x²-4). (x²-1)
= (x-2). (x+2). (x-1). (x+1)
8. 49- x²+ 2xy- y²= 49- (x²-2xy+y²)
= 7²- (x-y)²
= (7-x+y). (7+x-y)
9. x³- 4x²+ 5x-2= x³- 4x² +4x+x-2
= (x³- 4x²+4x)+ (x-2)
= x(x²- 4x+4)+ (x-2)
= x(x-2)²+ (x-2)
= (x-2). [x(x-2)+1]
= (x-2). (x²-2x+1)
= (x-2)(x-1)²
10. (x+1)(x+3)(x+5)(x+7)+15
= (x+1)(x+7)(x+3)(x+5)+15
= (x²+7x+x+7)(x²+5x+3x+15)+15
= (x²+8x+7)(x²+8x+15)+15
Đặt x²+8x+11=t, ta có:
(t-4)(t+4)+15
= t²-16+15
= t²-1
=(t-1)(t+1)
=(x²+8x+11-1)(x²+8x+11+1)
=(x²+8x+10)(x²+8x+12)
