Question

Найти значение выражения 25а^2-40ab+16b^2+5a-4b при a= 4b-1/5

Answer 1

$25 a^{2} -40ab+16b^{2} +5a-4b=(5a-4b)^{2} +5a-4b= \ =(5*(4b-0.2)-4b)^{2} +5*(4b-0.2)-4b= \ =(20b-1-4b)^{2} +20b-1-4b=(16b-1)^{2} +16b-1= \ =(16b-1)*(16b-1+1)=(16b-1)*16b=256b^{2} -16b$