How can we insert two independent random number to two equations (x,y) contain two parts like this:
x = a* randomnumber1 + b* randomnumber2
y = c* randomnumber1 + d* randomnumber2
these two random number should be independent.
Thank inadvance.

How are you generating your random numbers? Show your code please. Assuming you have assigned a random number (usually using the rand() function if C or C++) to randomnumber1 and randomnumber2, then your computation should be correct. You initialize your random number generator with a seed value - often the local time value, and then each call to rand() will produce a new (independent) value.

Your code is nearly correct but I am not 100% sure that it is giving your what your want:
So here is your code with some comments -- just to make sure:

// This line sets the random number seed.
// you only need this call once only in your code
srand(time(NULL));
// This is strange : -- your code produces a random
// number between 1.0 and 2.0. This is because rand() returns an
// integer between 0 and RAND_MAX so the division gives you
// a number between 0.0 and 1.0 and then you add 1.
float random1 = (float(rand())/(RAND_MAX)) + 1;
float random2 = (float(rand())/(RAND_MAX)) + 1;
// Now this is fine
x = a* random1 + b* random2;
// this line is strange becauses random1 and random2 have not changed.
// I expected to see ANOTHER copy of this:
random1= float(rand())/MAX_RAND +1.0;
y = c* random1 + d* random2;

If you test your code with* a and *b then same value as c and d, I expect you want a different value for x and y.

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