Sorry for slow reply. Didn't see you had replied as you hadn't quoted.
I'd think about the variables you need. In this case what does a triangle have... 3 sides. So you'd need a variable for each side. You'd also need a counter for amount of sides which are equal. Take the side inputs at the start
Side1 = Input "Enter side 1"
Side2 = Input "Enter side 2"
Side3 = Input "Enter side 3"
Then look at what the question asks you to do. Find out if the triangle entered is isosceles. This means you need to compare the entered side lengths and see if they are equal. You could either do that by writing out each comparison statement or using clever loops. We'll go with long list of statements as it is actually easier for this.
You'd need to compare the following sides
1-2
1-3
2-3
But it is no good comparing them unless you get an output from the comparison. IE if they are equal you want some sort of counter to increment so that when you're done with comparisons you have a total amount of sides which are equal. At the start of the algorithm set it to 0.
I'd use something like this:
If Side1 = Side2 then
Counter = Counter + 1
End If
If Side1 = Side3 then
Counter = Counter + 1
End If
If Side2 = Side3 then
Counter = Counter + 1
End If
You'd then end up with a number stored in the counter saying how many sides were equal. Check to see what this is and you'll find out if the triangle is isosceles. No sides equal or all sides equal will mean it isn't. 1 pair equal means it is.
If Counter = 1 then
Output "isosceles"
Else
Output "Not isosceles"
That should work. Don't forget start subroutine and end subroutine bits.