Question

if a-3b= 2 and ab= 5 then the value of a^3- 27^3 is

Answer 1

Answer:

a−3b=−6

Squaring both sides,

=>(a−3b)2=−62

=>a2+9b2−2(a)(3b)=36

=>a2+9b2−6(ab)=36

=>a2+9b2−6(−10)=36

=>a2+9b2=36−60

=>a2+9b2=−24

Now,

a3−(3b)3=(a−3b)[(a)2+(3b)2+(a)(3b)]

a3−27b3=−6(−24+3(−10))

                   =−6(−24−30)

                    =324