Phan tich da thuc thanh phan tu a) x^2-20x-125 b)12x^2-2x-4 c)3a^2-5ab-12b^2 d)25ab-6a^2+9b^2 03/08/2021 Bởi Ayla Phan tich da thuc thanh phan tu a) x^2-20x-125 b)12x^2-2x-4 c)3a^2-5ab-12b^2 d)25ab-6a^2+9b^2
a) $x^2-20x-125$ $=x^2-2.x.10+100-225$ $=(x-10)^2-15^2$ $=(x-10-15)(x-10+15)$ $=(x-25)(x-5)$ b) $12x^2-2x-4$ $=12x^2+6x-8x-4$ $=6x(2x+1)-4(2x+1)$ $=(2x+1)(6x-4)$ $=2(2x+1)(3x-2)$ c) $3a^2-5ab-12b^2$ $=3a^2-9ab+4ab-12b^2$ $=3a(a-3b)+4b(a-3b)$ $=(a-3b)(3a+4b)$ d) $25ab-6a^2+9b^2$ $=9b^2+27ab-2ab-6a^2$ $=9b(b+3a)-2a(b+3a)$ $=(b+3a)(9b-2a)$ Bình luận
Đáp án: Giải thích các bước giải: a)x² -20x -125 =x² +5x -25x -125 =x.(x+5) -25.(x+5) =(x+5).(x-25) b)12x² -2x -4 =12x² +6x -8x -4 =6x.(2x +1) -4.(2x +1) =(2x +1).(6x -4) c)3a² -5ab -12b² =3a² -9ab +4ab -12b² =3a.(a -3b) +4b.( a -3b) =(a -3b).(3a +4b) d)25ab -6a² +9b² =-2ab -6a² +27ab +9b² =-2a.(b +3a) +9b.(3a +b) =(3a +b).( 9b -2a) Bình luận
a) $x^2-20x-125$
$=x^2-2.x.10+100-225$
$=(x-10)^2-15^2$
$=(x-10-15)(x-10+15)$
$=(x-25)(x-5)$
b) $12x^2-2x-4$
$=12x^2+6x-8x-4$
$=6x(2x+1)-4(2x+1)$
$=(2x+1)(6x-4)$
$=2(2x+1)(3x-2)$
c) $3a^2-5ab-12b^2$
$=3a^2-9ab+4ab-12b^2$
$=3a(a-3b)+4b(a-3b)$
$=(a-3b)(3a+4b)$
d) $25ab-6a^2+9b^2$
$=9b^2+27ab-2ab-6a^2$
$=9b(b+3a)-2a(b+3a)$
$=(b+3a)(9b-2a)$
Đáp án:
Giải thích các bước giải:
a)x² -20x -125
=x² +5x -25x -125
=x.(x+5) -25.(x+5)
=(x+5).(x-25)
b)12x² -2x -4
=12x² +6x -8x -4
=6x.(2x +1) -4.(2x +1)
=(2x +1).(6x -4)
c)3a² -5ab -12b²
=3a² -9ab +4ab -12b²
=3a.(a -3b) +4b.( a -3b)
=(a -3b).(3a +4b)
d)25ab -6a² +9b²
=-2ab -6a² +27ab +9b²
=-2a.(b +3a) +9b.(3a +b)
=(3a +b).( 9b -2a)