Đáp án:
Giải thích các bước giải:
1.61
a) (x-9).(x-7)+1=(x-8-1).(x-8+1) +1=(x-8)² -1 +1=(x-8)²
b)x^6 -y^6 =(x³-y³).(x³+y³) =(x-y).(x² +x+1).(x+y).(x² -x+1)
c)(x² +x-1)² +4x² +4x
ko biết làm
1.62
a) (x+2y-3)² -4.(x+2y-3) +4
=(x+2y-3) -2.2.(x+2y-3) +2²
=(x+2y-3-2)²=(x+2y-5)²
b)(x-y)³-1 -3.(x-y).( x-y-1)
=(x-y-1).((x-y)² +(x-y) +1 ) -3.(x-y).(x-y-1)
=(x-y-1).( (x -y)² +x-y+1 -3x+3y )
=(x-y-1).( (x-y)² -2x +2y +1 )
1.63
(x²+y²-17 )² -4(xy-4)²
=(x²+y²-17 )² -2².(xy-4)²
=(x²+y²-17 )² -(2xy -8)²
=(x²+y²-17 -2xy +8).(x²+y²-17 +2xy-8)
=( (x-y)² -9 ).( (x+y)² -25) )
=(x-y-3).(x-y+3) .(x+y-5).(x+y+5)
1.64
a)x³ +15x²+75x+125=0
⇔x³ +3.x².5 +3.x.5² +5³=0
⇔(x+5)³ =0
⇔x+5=0
⇔x=-5
b) (x+2)³ +(x-3)³ =0
⇔(x+2 +x-3) .( (x+2)² -(x+2).(x-3) +(x-3)² )=0
⇔(2x -1).( (x+2)² -(x+2).(x-3) +(x-3)² )=0
⇔2x-1 =0 (vì ( (x+2)² -(x+2).(x-3) +(x-3)² ) > 0 )
⇔2x =1
⇔x =1/2
1.65 và 1.66 không biết làm.
