[m]y= ∫ y`dx= ∫ (-\frac{1}{7}cos(7x+7)+C_{1})=-\frac{1}{49}sin(7x+7)+C_{1}x+C_{2}[/m]
y(0)=7
y`(0)=7
[m]y(0)=-\frac{1}{49}sin(7\cdot 0+7)+C_{1}\cdot 0+C_{2}[/m] ⇒ [m]7=-\frac{1}{7}sin7+C_{2}[/m]
[m]y`(0)=\frac{1}{7}(-cos(7\cdot 0+7))+C_{1}[/m] ⇒ [m]7=-\frac{1}{7}cos7+C_{1}[/m]
⇒
[m]C_{1}=7+\frac{1}{7}cos7[/m]
[m]C_{2}=7+\frac{1}{7}sin7[/m]