Zad. 6
a)
u(x) = ax³ + x² - 6, w(x) = bx⁵ + 7x³ + x + 2
u(x) + w(x) = ax³ + x² - 6 + bx⁵ + 7x³ + x + 2 = bx⁵ + ax³ + 7x³ + x² + x - 4 =
= bx⁵ + (a + 7)x³ + x² + x - 4
[tex]\begin{cases} b \neq 0 \ \wedge \ a \in R &\text{} \Rightarrow st (u + w) = 5 \\ b = 0 \ \wedge \ a+7 \neq 0 &\text{} \Rightarrow st (u + w) = 3 \\ b = 0 \ \wedge \ a+7 =0 &\text{} \Rightarrow st (u + w) = 2 \end{cases} \Rightarrow \\\\ \Rightarrow \begin{cases} b \neq 0 \ \wedge \ a \in R &\text{} \Rightarrow st (u + w) = 5 \\ b = 0 \ \wedge \ a \neq - 7 &\text{} \Rightarrow st (u + w) = 3 \\ b = 0 \ \wedge \ a= -7 &\text{} \Rightarrow st (u + w) = 2 \end{cases}[/tex]
b)
u(x) = ax⁷ + 3x² + 4, w(x) = 3x⁷ - bx² - 5x + 6
u(x) + w(x) = ax⁷ + 3x² + 4 + 3x⁷ - bx² - 5x + 6 = ax⁷ + 3x⁷ + 3x² - bx² - 5x + 10
= (a + 3)x⁷ + (3 - b)x² - 5x + 10 = (a + 3)x⁷ - (b - 3)x² - 5x + 10
[tex]\begin{cases} a + 3 \neq 0 \ \wedge \ b \in R &\text{} \Rightarrow st (u + w) = 7 \\ a+3 = 0 \ \wedge \ b-3 \neq 0 &\text{} \Rightarrow st (u + w) = 2 \\ a+3 = 0 \ \wedge \ b-3 =0 &\text{} \Rightarrow st (u + w) = 1 \end{cases} \Rightarrow \\\\ \Rightarrow \begin{cases} a \neq - 3 \ \wedge \ b \in R &\text{} \Rightarrow st (u + w) = 7 \\ a= -3 \ \wedge \ b\neq 3 &\text{} \Rightarrow st (u + w) = 2 \\ a=-3 \ \wedge \ b=3 &\text{} \Rightarrow st (u + w) = 1 \end{cases}[/tex]
c)
u(x) = (a + 1)x⁴ - bx³ + 2x² + 1, w(x) = (- 1 - b)x⁴ - 4x³ - 2x² + 9x
u(x) + w(x) = (a + 1)x⁴ - bx³ + 2x² + 1 + (- 1 - b)x⁴ - 4x³ - 2x² + 9x = (a + 1)x⁴ +
+ (- 1 - b)x⁴ - bx³ - 4x³ + 2x² - 2x² + 9x + 1 = (a + 1 - 1 - b)x⁴ - (b + 4)x³ + 9x + 1 =
= (a - b)x⁴ - (b + 4)x³ + 9x + 1
[tex]\begin{cases} a -b \neq 0 \ \wedge \ b \in R &\text{} \Rightarrow st (u + w) = 4 \\ a-b = 0 \ \wedge \ b+4 \neq 0 &\text{} \Rightarrow st (u + w) = 2 \\ a-b= 0 \ \wedge \ b+4 =0 &\text{} \Rightarrow st (u + w) = 1 \end{cases} \Rightarrow \\\\ \Rightarrow \begin{cases} a \neq b \ \wedge \ b \in R &\text{} \Rightarrow st (u + w) = 4 \\ a=b \ \wedge \ b\neq -4 &\text{} \Rightarrow st (u + w) = 2 \\ a= b \ \wedge \ b=-4 &\text{} \Rightarrow st (u + w) = 1 \end{cases} \Rightarrow[/tex]
[tex]\Rightarrow \begin{cases} a \neq b &\text{} \Rightarrow st (u + w) = 4 \\ a=b \neq -4 &\text{} \Rightarrow st (u + w) = 2 \\ a= b =-4 &\text{} \Rightarrow st (u + w) = 1 \end{cases}[/tex]