Question 163546
1.{{{sin(a+b)=sin(a)cos(b)+cos(a)sin(b)}}}
{{{sin(x^2+1)=sin(x^2)cos(1)+cos(x^2)sin(1)}}}
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2.{{{tan(a+b)=(tan(a)+tan(b))/(1-tan(a)tan(b))}}}
{{{tan(x+2)=(tan(x)+tan(2))/(1-tan(x)tan(2))}}}
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3.Yes, you can calculate the slope from the two points.
Then use the point-slope form of a line.
First, the slope,
{{{m=(y[2]-y[1])/(x[2]-x[1]))}}}
{{{m=(3-(-5))/(3-(-1)))}}}
{{{m=8/4)}}}
{{{m=2}}}
Now that you have the slope, use the point-slope form,
{{{y-y[p]=m(x-x[p])}}}
You can use either point. 
{{{y-3=2(x-3)}}}
{{{y-3=2x-6}}}
{{{y=2x-3}}}
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Here's graphical verification. 
{{{drawing( 300, 300, -5, 5, -5, 5,grid( 1 ),circle(-1,-5,.2),circle( 3, 3, .2 ),green(line( 10, 17, -10, -23)))}}}