Combinatorial Enumeration. That whole class was a rollercoaster ride of mind-blowing generating functions to prove crazy things. The exam had ridiculous questions like 'count the number of cactus trees with n vertices such that etc etc etc' and you'd do three pages of terrible terrible sums and algebra. Then your final answer would be something beautiful like n/2 and you'd breath a sigh of relief and thank the math gods.
 
        
             
        
        
        
Am i supposed to multiply? 5 times 3 equals 15 
        
                    
             
        
        
        
Triangle ABE is isosceles  / Given
AB congruent to AE     / Def isosceles
angle ABE congruent to angle AEB   / Property of isosceles triangles
angle ABD congruent to angle AEC   / Subst different name for same angles
BD congruent to EC     / Given
triange ABD congruent to triange AEC    / Side Angle Side
 
        
             
        
        
        
-x + 5y = 8 
multiply this equation by 3
-3x + 15y = 24
now add it to the other equation  ( elimination)
-3x + 15y = 24
 3x + 7y = -2
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0x  + 22 y = 22
divide each side by 22
y =1
substitute into -x + 5y =8  to find x
-x + 5(1) = 8
-x + 5 = 8
-x =3
divide by -1
x =-3
Answer (-3,1)
Choice A