Подстановка условия
[src](2*a + b)*(c - a) + (b + c)*(a + b) при a = 3
(2*a + b)*(c - a) + (b + c)*(a + b)
$$\left(- a + c\right) \left(2 a + b\right) + \left(a + b\right) \left(b + c\right)$$
(2*(3) + b)*(c - (3)) + (b + c)*((3) + b)
$$\left(- (3) + c\right) \left(2 (3) + b\right) + \left((3) + b\right) \left(b + c\right)$$
(2*3 + b)*(c - 3) + (b + c)*(3 + b)
$$\left(b + 3\right) \left(b + c\right) + \left(b + 2 \cdot 3\right) \left(c - 3\right)$$
(-3 + c)*(6 + b) + (3 + b)*(b + c)
$$\left(b + 3\right) \left(b + c\right) + \left(b + 6\right) \left(c - 3\right)$$