If $a^2 + b^2 + c^2 + 170 = 2 (8a + 5b - 9c)$, then the value of $\sqrt{4a+8b-c}$ will be :

9

If $a^2 + b^2 + c^2 + 170 = 2 (8a + 5b - 9c)$,

then the value of $\sqrt{4a+8b-c}$ will be = ?

we can find the values of the variables by =

Coefficient of variables on right sides divide by coefficient of same variable on left side along with the signs as given below = 

a = 8

b = 5

c = -9

Put them in the  required equation,

$\sqrt{4a+8b-c}$= $\sqrt{4(8)+8(5)-(-9)}$ 

= $\sqrt{32+40+9}$  = $\sqrt{81}$ = 9