Question

if 2a - b - 6c=4 and 4a²+b²+36c²=18 find the value of -2ab+6bc-12ac​

Answer 1

Answer:

(2a-b-6c)=4

Squaring both sides,

(2a-b-6c)²=4²

(2a)²+(-b)²+(-6c)²+2×2a(-b)+2(-b)(-6c)+2(-6c)×2a=16

4a²+b²+36c²-4ab+12bc-24ca=16

18+2(-2ab+6bc-12ac)=16

2(-2ab+6bc-12ac)=16-18

2(-2ab+6bc-12ac)= - 2

-2ab+6bc-12ac= - 2/2

-2ab+6bc-12ac= - 1