Let the slope of the curve y=x3+ax−b be m1
∴dydx=3x2+a(dydx)(1,−5)=3+a=m1
Slope of line, −x+y+4=0 is m2=1
Since, the given line is perpendicular to the tangent to the given curve at (1,−5)
∴m1×m2=−1⇒(3+a)(1)=−1⇒a=−4
Also, (1,−5) lies on graph.
∴−5=(1)3+a(1)−b⇒−6=−4−b ⇒b=2
∴y=x3−4x−2=0
∴(2,−2) lies on y=x3−4x−2=0