Question

If y = 5 - cube √ ( 25 ) - cube √ (5), then find the value of y ^ 3 - 15y ^ 2 + 60y + 40

Answer 1

Given y =5-∛25-∛5

          y-5 = -(∛25+∛5)

Cubing on both sides gives

 ⇒(y-5)³=-(∛25+∛5)³

⇒y³-125-15y(y-5) = -[25+5+15(5-y)]   ∵-(∛25-∛5) = y-5

⇒y³-125-15y²+75y=- [105-15y]

⇒y³-15y²+60y+40=125-105

⇒y³-15y²+60y+40=20

∴y³-15y²+60y+40 = 180

Answer 2

answer of this question is must be 60