Slope of the tangent line to the parabola Problem

[killasnake]

The slope of the tangent line to the parabola y=4x^+3x+6 at the point (5,121) is _ 43__
The equation of this tangent line can be written in the form y=mx+b where m is_43_ and where B is:______

I need help to solving b, what I did was

121 = 43(5)+b

121 = 215 +b

b= .562790??

Is that right? I tried submiting the asnwer but it is wrong.

 

[arthur ohlsten]

y=4x^2+3x+6

A tangent line has the slope:
dy/dx= 8x+3 and at the point x=5 y=[100+15+6] y=121 the slope is
dy/dx= 43 and this is the slope m of the tangent line

=============================================
the equation of the tangent line is:
y=mx+b but the slope m=43 or:
y=43x+b but the line passes thru the point x=5 y=121 substitute and solve for b
121=43[5]+b
121=215+b subtract 215 from each side, ( don't divide)
b=-94

the equation of the tangent line is
y=43x -94

 

[killasnake]

121=215+b subtract 215 from each side, ( don't divide)

Oh I divided that why I got such a small decimal answer

Thank you!