Verified answer

1)

[tex]5b3b - 4c3b - 5b2c - 4c( - 2)c = 15 {b}^{2} - 12cb - 10bc + 8 {c}^{2} = \\ \\ = 15 {b}^{2} - 22bc + 8 {c}^{2} [/tex]

2)

[tex]b8b - 3c8b + 5cb - 3c5c = 8 {b}^{2} - 24cb + 5cb - 15 {c}^{2} = 8 {b}^{2} - 19cb - 15 {c}^{2} [/tex]

3)

[tex]6 {a}^{2} 2 {a}^{2} + 5 {b}^{2} 2 {a}^{2} - 6 {a}^{2} 4 {b}^{2} - 5 {b}^{2} 4 {b}^{2} = 12 {a}^{4} + 10 {b}^{2} {a}^{2} - 24 {a}^{2} {b}^{2} - 20 {b}^{4} = \\ \\ = 12 {a}^{4} - 14 {a}^{2} {b}^{2} - 20 {b}^{4} [/tex]

4)

[tex]2 {x}^{2} \frac{1}{2} y - \frac{1}{3} ab3a + 1 \frac{1}{4} y \frac{4}{5} {x}^{2} + aab = {x}^{2} y - {a}^{2} b + y {x}^{2} + {a}^{2} b = 2 {x}^{2} y[/tex]