Mathcad 14: "pattern match exception" when solving equation with more unknowns

Question

I'm trying to solve an equation with 5 unknowns in Mathcad 14. My equations look like this:

 Given
 0 = e
 1 = d
 0 = c
 -1 = 81a + 27b + 9c + 3d + e
 0 = 108a + 27b + 6c + d
 Find(a,b,c,d,e)

Find(a,b,c,d,e) is marked as red and says "pattern match exception". What is the problem?

Answer 1

In mathcad you need to do something similar to:

c:=0
d:=1
e:=0
a:=1
b:=1

Given

81*a + 27*b + 9*c + 3*d + e = -1
108*a + 27*b + 6*c + d = 0

Find(a,b,c,d,e) = (0,0,0,0,-1)

Now, what I have done here is to define the variables BEFORE the Solve Block (Given...Find), you have to give initial values which you think are close to the solution you require in order for the iteration to succeed.

Tips: To get the equals sign in the Solve Block, use ctrl and '='. If your looking to solve for 5 unknowns then you need 5 equations, the original post looked like you knew 3 of the variables and were looking for a and b, in this case you would do the following:

c:=0
d:=1
e:=0
a:=1
b:=1

Given

81*a + 27*b + 9*c + 3*d + e = -1
108*a + 27*b + 6*c + d = 0

Find(a,b) = (0.111,-0.481)

This has held c, d and e to their original values and iterated to solve for a and b only.

Hope this helps.