Phân tích đa thức thành nhân tử : x^2 – 8x -9 3x^2 – 5x -2 x^2 -x – 6 4x^2 -36x + 56 giải hộ mk 16/07/2021 Bởi Charlie Phân tích đa thức thành nhân tử : x^2 – 8x -9 3x^2 – 5x -2 x^2 -x – 6 4x^2 -36x + 56 giải hộ mk
a. $x^{2}-8x-9= x^{2}-8x+16-25= (x-4)^{2} – 5^{2}= (x-4-5).(x-4+5)= ( x-9).(x+1)$ b. $3x^2 – 5x -2 ^{}= 3x^{2}+x-6x-2 = (3x^{2}+x)-(6x+2)= x(3x+1)-2(3x+1)= (3x+1).(x-2)$ c. $x^{2}-x-6= x^{2} – 2.1.$ $\frac{1}{2}.x + $ ($\frac{1}{2})^{2}-$ $\frac{25}{4}= ( x- $ $\frac{1}{2})^{2}-($ $\frac{5}{2})^{2}= (x-$ $\frac{1}{2}-$ $\frac{5}{2}).(x-$ $\frac{1}{2}+$ $\frac{5}{2})= (x – 3).(x + 2) $ d. $4x^2 -36x + 56^{}= (2x)^{2}-2.2x.9+9^{2}-25=( 2x-9)^{2} – 5^{2} = ( 2x – 9 – 5 ).(2x – 9 + 5)= (2x -14) .(2x -4) $ Bình luận
Đáp án: x² – 8x – 9 = x² – x + 9x – 9 = x(x – 1) – 9(x – 1) = (x – 1) ( x – 9) 3x² – 5x – 2 = 3x² – 3x – 2x – 2 = 3x(x – 1) – 2(x – 1) = (x – 1) (3x – 2) x² – x – 6 = x² – 2x + 2x – 6 = x(x – 2) – 2(x – 3) = (x – 2)(x – 3) 4x² – 36x + 56 = 4(x² – 9x + 14) = 4(x² – 2x – 7x + 14) = 4[x(x – 2) – 7(x – 2)] = 4(x – 2) (x – 7) Bình luận
a. $x^{2}-8x-9= x^{2}-8x+16-25= (x-4)^{2} – 5^{2}= (x-4-5).(x-4+5)= ( x-9).(x+1)$
b. $3x^2 – 5x -2 ^{}= 3x^{2}+x-6x-2 = (3x^{2}+x)-(6x+2)= x(3x+1)-2(3x+1)= (3x+1).(x-2)$
c. $x^{2}-x-6= x^{2} – 2.1.$ $\frac{1}{2}.x + $ ($\frac{1}{2})^{2}-$ $\frac{25}{4}= ( x- $ $\frac{1}{2})^{2}-($ $\frac{5}{2})^{2}= (x-$ $\frac{1}{2}-$ $\frac{5}{2}).(x-$ $\frac{1}{2}+$ $\frac{5}{2})= (x – 3).(x + 2) $
d. $4x^2 -36x + 56^{}= (2x)^{2}-2.2x.9+9^{2}-25=( 2x-9)^{2} – 5^{2} = ( 2x – 9 – 5 ).(2x – 9 + 5)= (2x -14) .(2x -4) $
Đáp án:
x² – 8x – 9
= x² – x + 9x – 9
= x(x – 1) – 9(x – 1)
= (x – 1) ( x – 9)
3x² – 5x – 2
= 3x² – 3x – 2x – 2
= 3x(x – 1) – 2(x – 1)
= (x – 1) (3x – 2)
x² – x – 6
= x² – 2x + 2x – 6
= x(x – 2) – 2(x – 3)
= (x – 2)(x – 3)
4x² – 36x + 56
= 4(x² – 9x + 14)
= 4(x² – 2x – 7x + 14)
= 4[x(x – 2) – 7(x – 2)]
= 4(x – 2) (x – 7)