Question

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Answer 1

The expression to differentiate includes
`cos(x)`.

Remember that the derivative of
`cos(x)` is
`-sin(x)`.

Put another way,
`(d)/(dx)[cos(x)]=- sin(x)`


`(d)/(dx)[cos(x)-7x]`


`(d)/(dx)[cos(x)]-7 (d)/(dx)(x)`


`-sin(x) -7*1`


`-sin(x)-7`

In conclusion,
`(d)/(dx)[\cos(x)-7x]=-\sin(x)-7`