rut gon cac bieu thuc sau:
a,(x+1)^2-(x-1)^2 -3*(x+1)*(x-1)
b,5*(x+2)*(x-2)-1phần 2*(6-8x)^2+17
rut gon cac bieu thuc sau: a,(x+1)^2-(x-1)^2 -3*(x+1)*(x-1) b,5*(x+2)*(x-2)-1phần 2*(6-8x)^2+17
By Arianna
By Arianna
rut gon cac bieu thuc sau:
a,(x+1)^2-(x-1)^2 -3*(x+1)*(x-1)
b,5*(x+2)*(x-2)-1phần 2*(6-8x)^2+17
a) $(x+1)^2-(x-1)^2-3.(x+1)(x-1)$
$=x^2+2x+1-x^2+2x-1-3(x^2-1)$
$=(x^2-x^2)+(2x+2x)+(1-1)-3x^2+3$
$=4x-3x^2+3$
b) $5(x+2)(x-2)-\dfrac{1}{2}.(6-8x)^2+17$
$=5.(x^2-4)-\dfrac{1}{2}.(36-96x+64x^2)+17$
$=5x^2-20-18+48x-32x^2+17$
$=(5x^2-32x^2)+(-20-18+17)+48x$
$=-27x^2+48x-21$
Đáp án:
\(\begin{array}{l} a,\ (x+1)^2-(x-1)^2-3(x+1)(x-1)=-3x^2+4x+3\\ b,\ 5(x+2)(x-2)-\dfrac12(6-8x)^2+17=-27x^2+48x-21\end{array}\)
Giải thích các bước giải:
\(\begin{array}{l} a,\ (x+1)^2-(x-1)^2-3(x+1)(x-1)\\ =x^2+2x+1-x^2+2x-1-3(x^2-1)\\ =x^2+2x+1-x^2+2x-1-3x^2+3\\ =(x^2-x^2-3x^2)+(2x+2x)+(1-1+3)\\ =-3x^2+4x+3\\ b,\ 5(x+2)(x-2)-\dfrac12(6-8x)^2+17\\ =5(x^2-4)-\dfrac12(36-96x+64x^2)+17\\ =5x^2-20-18+48x+32x^2+17\\ =(5x^2-32x^2)+48x+(-20-18+17)\\ =-27x^2+48x-21\end{array}\)
chúc bạn học tốt!