How to find a third point using two other points and their angle - objective-c

Question

I found an answer here, but can't understand how to transfer the math to Objective C
Find the third point
I have two points and I also have the angle relative to the axes. How do I find a third point which will form a straight line? The distance should be variable.

Answer 1

This is the code that I am using:
float distanceFromPx2toP3 = 1300.0;
float mag = sqrt(pow((px2.x - px1.x),2) + pow((px2.y - px1.y),2));
float P3x = px2.x + distanceFromPx2toP3 * (px2.x - px1.x) / mag;
float P3y = px2.y + distanceFromPx2toP3 * (px2.y - px1.y) / mag;
CGPoint P3 = CGPointMake(P3x, P3y);

Answer 2

Let's say I have two points pointA and pointB. The slope of the line formed by the two points m is:
static CGFloat calculateSlope(CGPoint pointA, CGPoint pointB) {
CGFloat m = (pointB.y - pointA.y) / (pointB.x - pointA.x);
return m;
}
A third point pointC a distance d from pointA on the line would be given by:
static CGPoint calculatePointOnLine(
CGPoint pointA, CGPoint pointB, CGFloat d, BOOL startAtB) {
CGFloat m = calculateSlope(pointA, pointB);
CGFloat dX = pointB.x - pointA.x;
CGFloat dY = pointB.y - pointA.y;
CGFloat signDX = dX / fabsf(dX);
CGFloat signDY = dY / fabsf(dY);
CGFloat dSquared = d * d;
CGFloat mSquared = m * m;
// We know pointC is distance d from pointA,
// and that pointA and pointC are on the
// same line
// dXSquared + dYSquared = dSquared
// m = dY / dX
// dY = m * dX
// dXSquared + mSquared * dXSquared = dSquared
// dXSquared * ( 1 + mSquared ) = dSquared
// dXSquared = dSquared / ( 1 + mSquared )
// Handle a vertical line, dX == 0, and a horizontal line, dY == 0
if (dX != 0 && dY != 0) {
// Account for the sign of dX
dX = signDX * sqrtf(dSquared / ( 1 + mSquared ));
// Account for the sign of dY
dY = signDY * m * dX;
}
// Handle a vertical line, dX == 0
if (dX == 0 && dY != 0) {
dY = signDY * d;
}
// Handle a horizontal line, dY == 0
if (dY == 0 && dX != 0) {
dX = signDX * d;
}
CGPoint startingPoint = pointA;
if (startAtB) {
startingPoint = pointB;
}
CGPoint pointC = CGMakePoint(startingPoint.x + dX,
startingPoint.y + dY);
return pointC;
}
pointC will now always lie a distance d along the line from pointA,
in the direction from pointA to pointB. Pass startAtB to have pointC
lie a distance d along the line from pointB, in the direction from
pointA to pointB.
Exchange the order of piintA and pointB in the call to calculatPointOnLine
to calculate a pointC which lies a distance d along the line from
PointB, in the direction from pointB to pointA.
You can use these two functions to calculate a third point on the line.
Thanks for accepting this answer if this helps you.