a/ \(\left(-2x^2y\right)5xy^4\)

\(=-10x^3y^5\)

tự lm tiếp, rất dễ

a: \(A=\left(-\frac25x^2y\right)\cdot\left(\frac{15}{8}xy^2\right)\left(-x^3y^2\right)\)

\(=\frac25\cdot\frac{15}{8}\cdot x^2\cdot x\cdot y\cdot y^2\cdot x^3\cdot y^2=\frac{30}{40}x^6y^5=\frac34x^6y^5\)

\(B=\left(xy\right)^2\cdot\frac58x^2y^3\)

\(=x^2y^2\cdot\frac58x^2y^3=\frac58x^4y^5\)

b: \(A=\frac34x^6y^5\)

Hệ số là 3/4

Phần biến là x^6;y^5

Bậc là 6+5=11

\(B=\frac58x^4y^5\)

Hệ số là 5/8

Phần biến là \(x^4;y^5\)

Bậc là 4+5=9

Đặt \(\dfrac{x}{4}=\dfrac{y}{7}=k\Rightarrow x=4k.y=7k\)

Ta có:\(y^2-x^2=66\\ \Rightarrow\left(7k\right)^2-\left(4k\right)^2=66\\ \Rightarrow49k^2-16k^2=66\\ \Rightarrow33k^2=66\\ \Rightarrow k^2=2\\ \Rightarrow\left[{}\begin{matrix}k=\sqrt{2}\\k=-\sqrt{2}\end{matrix}\right.\\ \Rightarrow\left[{}\begin{matrix}x=4\sqrt{2};y=7\sqrt{2}\\x=-4\sqrt{2};y=-7\sqrt{2}\end{matrix}\right.\)

,(3x-1) mũ 2=9/16
<=> (3x-1)^2 = ( ±3/4)^2
<=> l3x-1l  = 3/4
Hoặc 3x-1 = 3/4
 <=> 3x= 3/4 + 1
<=> x = 7/4 : 3
<=> x= 7/1

Bài 1: 

a) Ta có: \(\left(15x^2\cdot y^2\cdot z\right):3xyz\)

\(=\dfrac{15x^2y^2z}{3xyz}\)

\(=5xy\)

b) Ta có: \(3x^2\cdot\left(5x^2-4x+3\right)\)

\(=3x^2\cdot5x^2-3x^2\cdot4x+3x^2\cdot3\)

\(=15x^4-12x^3+9x^2\)

c) Ta có: \(\left(2x^2-3x\right):\left(x-4\right)\)

\(=\dfrac{2x^2-8x+5x-20+20}{x-4}\)

\(=\dfrac{2x\left(x-4\right)+5\left(x-4\right)+20}{x-4}\)

\(=2x+5+\dfrac{20}{x-4}\)

d) Ta có: \(-5xy\cdot\left(3x^2y-5xy+y^2\right)\)

\(=-5xy\cdot3x^2y+5xy\cdot5xy-5xy\cdot y^2\)

\(=-15x^3y^2+25x^2y^2-5xy^3\)