A classmate is working on the following problem and his answer is incorrect:
dx
d​ [ x 2 −13x−5​ ]= (x 2 −1) 2 (3x−5)(2x)−(x 2 −1)3​ = (x 2 −1) 2 0x 2 −10x−3x2 +3
​ = (x 2 −1) 2 3x 2 −10x+3
​
Find the correct derivative. Explain the error that your classmate made.