The Total solution for NCERT class 6-12
a – b = 4, ab= 21Cubing both sides,⇒ (a –A)3 = (4)3⇒ a3 –b3 – 3ab (a – b) = 64⇒ a3-i3-3×21x4 = 64⇒ a3 – 63 – 252 = 64⇒ a3 – 63 = 64 + 252 =316∴ a3 –b3 = 316