SSC CPO SI and ASI Model Paper 2

Question : 105 of 200

Marks: +1, -0

If 2x – 3y = 5, then what is the value of $8x^3–27y^3– 90xy + 125 ?$

Solution:

(3) 2x – 3y = 5
By cubing both sides:

(2x – 3y)^3 = 5^3

8x^3–27y^3–3–(2x)(3y)(2x–3y)=125

8x^3–27y^3–3 (2x)(3y)(5)= 125

8x^3–27y^3–90xy=125

∴ 8x^3–27y^3–90xy + 125=250

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