(1 point) Solve the initial value problem yy' + x = \\/ x + y with y(1) = -V15. a. To solve this, we should use the substitution u = x12+y12 help (formulas) u'= 2x+2y y' help (formulas) Enter derivatives using prime notation (e.g., you would enter y for dy dx) b. After the substitution from the previous part, we obtain the following linear differential equation in x, u, u'. 1/2 u'=sqrtu help (equations) c. The solution to the original initial value problem is described by the following equation in x, y. y=sqrt(9+6x) help (equations)