Question

If x+y=9 and xy=20 find (x+y)^3

Answer 1

Solution :-

Given ,

• x + y = 9
• xy = 20

We need to find ,

• ( x + y ) ³

Method of solving ,

• By cubing on both sides of the given equation.

___________________

Given equation ,

x + y = 9

On cubing on both sides ,

⇒ ( x + y )³ = 9³

⇒ ( x + y )³ = 729

Hence , ( x + y )³ = 729

Answer 2

Answer:

729

Step-by-step explanation:

x+y=9 ---(1)

xy=20 ----(2)

x=9-y

Substitute this value in equation (2)

which will then be

(9-y)(y)=20

9y-y^2=20

9y-y^2-20=0

y^2-9y+20=0

y^2-4y-5y+20=0

y(y-4)-5(y-4)=0

(y-5)(y-4)=0

y=5 ,4

Choose any of the two value and substitute in equation (1) both would work,I am taking the value 5

x+5=9

x=9-5

x=4

now that you have both the value

put them in the equation

(x+y)^3

(4+5)^3

(9)^3

729

Hope it helped