Explanation

y = cos 3x Let u = 3x so that y = cos u Now, δy/δx = 3, δy/δx = −sinu By the chain rule, δy/δx=δy/δu × δu/δx δy/δx = (−sinu)(3) δy/δx = −3sinu δy/δx= −3sin3x

y = cos 3x Let u = 3x so that y = cos u Now, δy/δx = 3, δy/δx = −sinu By the chain rule, δy/δx=δy/δu × δu/δx δy/δx = (−sinu)(3) δy/δx = −3sinu δy/δx= −3sin3x