Question

find the value of x^3+y^3+15xy-125 if x+y=5
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Answer 1

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:

Step-by-step explanation:

0 is the correct answer

(x+y)^3=(5)^3 -(on cubing both the sides)

x3+y3+3xy(x+y)=125

x^3+y^3+3xy*5=125

x^3+y^3+15xy-125=0

hence prved!!!!