Toán Lớp 8: Bài 7: thực hiện phép tính:
A. 2x/3 : 5/6x^2
B. x^2-y^2/6x^2y : x+y/3xy
C. x+y/y-x : x^2+xy/3x^2-3y^2
Leave a reply
Register Now
Login
Lost Password
Lost your password? Please enter your email address. You will receive a link and will create a new password via email.
Toán Lớp 8: Bài 7: thực hiện phép tính:
A. 2x/3 : 5/6x^2
B. x^2-y^2/6x^2y : x+y/3xy
C. x+y/y-x : x^2+xy/3x^2-3y^2
Comments ( 2 )
a. (2x)/3 : (5)/(6x^2)
= (2x)/3 . (6x^2)/5
= (12x^3)/15
= (4x^3)/5
b. (x^2 – y^2)/(6x^2y) : (x+y)/(3xy)
= [(x – y).(x+y)]/(6x^2y) . (3xy)/(x+y)
= (x-y)/(2x)
c. (x+y)/(y-x) : (x^2 + xy)/(3x^2 – 3y^2)
= (x+y)/(y-x) . [-3.(y-x)(x+y)]/[x.(x+y)]
= [-3.(x+y)]/x
* Áp dụng hằng đằng thức: A^2 – B^2 = (A+B).(A-B).
$a)$ $\dfrac{2x}{3}\::\:\dfrac{5}{6x^2}$
$=\dfrac{2x\cdot \:6x^2}{3\cdot \:5}$
$=\dfrac{4x^3}{5}$
____________________________
$b)$ $\dfrac{x^2-y^2}{6x^2y}:\dfrac{x+y}{3xy}$
$=\dfrac{\left(x^2-y^2\right)\cdot \:3xy}{6x^2y\left(x+y\right)}$
$=\dfrac{x-y}{2x}$
____________________________
$c)$ $\dfrac{\:x+y}{y-x}:\dfrac{x^2+xy}{3x^2-3y^2}$
$=\dfrac{\left(x+y\right)\left(3x^2-3y^2\right)}{\left(y-x\right)\left(x^2+xy\right)}$
$=-\dfrac{\left(x+y\right)\cdot \:3}{x}$
$=-\dfrac{3\left(x+y\right)}{x}$