Question

find the value of x^3+y^3+15xy-125 if x+y=5

Answer 1

Answer:

Step-by-step explanation:

Given that x+y=5

cube both sides:

(x+y)^3=x^3+y^3+3xy(x+y)

125=x^3+y^3+3xy(5)

hence

x^3+y^3+15xy=125

so the required expression is x^3+y^3+15xy-125=125–125=0

Answer 2

Answer: x + y = 5

Step-by-step explanation:

X = 5 -y..... (1)

X3+y3+15xy-125........(2)

(1)in(2)

(5-y)^3+y^3+15y(5-y)-125

After expanding (5-y)3 you will get

125-15y(5-y)+y3-y3+15(5-y)y+125=0

Hope it helps...