y = x

`y' = cos(x) + 2sin(x)cos(x).`

x = 0

`y' = 1 + 0 = 1`

Substituting into the y-intercept form of the line,

`y = 1x + 0 = x`

y = x

`y' = cos(x) + 2sin(x)cos(x).`

x = 0

`y' = 1 + 0 = 1`

Substituting into the y-intercept form of the line,

`y = 1x + 0 = x`