Solve squared (non-linear) system with two equations

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I want to solve this two non-linear equations for t1 and t2 and do an implementation in C++ afterwards. (Only with the solution functions for t1,t2 only).

Each of the equations should result in 2 solutions, therefore at all 4 solution.

I:  x1*t1^2 + y1*t1 - x3*t2^2 - y3*t2 + z1 == 0
II: x2*t1^2 + y2*t1 - x4*t2^2 - y4*t2 + z2 == 0

x1,x2,x3,x4,y1,y2,y3,y4,z1,z2 are known
t1,t2 are only unknown and should be calculated

In Matlab is is possible to solve it easily with

solve(I,II,[t1 t2])

, but I am not able to to is by hand to get the 4 equations to calculate t1/t2.

How can I do this? Or which kind of topic is this problem?

Update:

My question is based on the following solution for the intersection of two rotated parabola, which results in

0 = xa'(t1) - xb'(t2)
0 = ya'(t1) - yb'(t2)

In this solution he describes:

Each of these equation is just a order 2 polynomial. These are easy to solve.