Question

If a − b = −8 and ab  = −12, then a³ − b³ =

पर्याय

• −244

•  −240

• −224

• −260

Answer 1

To find the value of a³ − b³ 

Given  `a-b = -8,ab =-12`

Using identity `(a-b)^3 = a^3 - b^3 -3ab(a-b)`

Here `a-b = -8,ab =-12`we get 

`(-8)^3 = a^3 -b^3 -3ab(a-b)`

`(-8)^3 =a^3 -b^3 -3 xx -12 xx -8`

`-512 = a^3 -b^3 - 288`

Transposing -288 to left hand side we get  

`- 512 + 288 = a^3 - b^3`

`-224 = a^3 - b^3`

Hence the value of  `a^3 -b^3 `is  -224 .