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 #1
avatar+9491 
+4

I found this diagram from here: https://www.mathisfunforum.com/viewtopic.php?id=22434

 

 

There are  180°  in every triangle.  So..

 

m∠BDC+m∠BCD+ m∠CBD=180°  
                                      The problem says that  m∠CBD  =  28°
m∠BDC+m∠BCD+28°=180°  
        Since  BD  =  BC,  m∠BCD  =  m∠BDC
m∠BDC+m∠BDC+28°=180°  
         
2(m∠BDC)+28°=180°  
        Subtract  28°  from both sides.
2(m∠BDC)  =152°  

 

       

Divide both sides of the equation by  2  .

  m∠BDC  =76°  

 

 

And since  m∠BDC  and  m∠BDE  form a straight line, they sum to  180° .

 

76°  +  m∠BDE  =  180°

                                              Subtract  76°  from both sides.

            m∠BDE  =  104°

 

 

In a parallelogram, opposite angles are congruent. Imagine sliding up ED onto AB and sliding over BD onto AE. Then you can see that they are vertical angles, so they have the same measure.

 

m∠BDE  =  m∠BAE  =  104°

Aug 7, 2017
Aug 6, 2017
 #2
avatar+2446 
+2

I would argue that there is a second solution to this problem, however. Let me demonstrate why:
 

\((x+a)^2=x^2+10x+25\) Take the square root of both sides of the equation. Of course, taking the square root of a number results in a positive and a negative answer.
\(x+a=\pm\sqrt{x^2+10x+25}\) Let's split these solutions into 2
\(x+a=\sqrt{x^2+10x+25}\) \(x+a=-\sqrt{x^2+10x+25}\)

 

 
   

 

Now, let's solve each equation separately:

 

\(x+a=\sqrt{x^2+10x+25}\) The first step is to factor the expression x^2+10x+25. Now, this trinomial is indeed a perfect-square trinomial. I know this because x^2 and 25 are perfect squares; x and 5. If you multiply the sum of x and 5 by 2, then you get 10x. If this condition is ever true with a trinomial, you have a perfect-square trinomial.
\(x+a=\sqrt{(x+5)^2}\) The square root and the square cancel each other out.
\(x+a=x+5\) Subtract x on both sides.
\(a=5\)  
   

 

You will notice that the user above also got this answer of a=5. What about the second solution? Well, you'll see. Solve for a in the following equation \(x+a=-\sqrt{x^2+10x+25}\), the second case:

 

\(x+a=-\sqrt{x^2+10x+25}\) We have already determined previously that \(\sqrt{x^2+10x+25}\) equals \(x+5\). Let's just plug that in to save a few steps.
\(x+a=-(x+5)\) Distribute the negative sign to both terms.
\(x+a=-x-5\) Subtract x on both sides.
\(a=-2x-5\)  
   

 

Is this actually a solution, though? If you are ever unsure of whether or not a solution is truly a solution, plug it into the original equation:

 

\((x+a)^2=x^2+10x+25\) Substitute a for -2x-5
\((x+(-2x-5))^2=x^2+10x+25\) Combine the terms of x and -2x
\((-x-5)^2=x^2+10x+25\) Expand (-x-5)^2 using the rule that \((a+b)^2=a^2+2ab+b^2\)
\(x^2+10x+25=x^2+10x+25\) Both sides of the equation are the same, so it should be clear now that both are equivalent. Therefore, -2x-5 is a solution.
   

 

Therefore, there are two solutions

 

\(a_1=5\)

\(a_2=-2x-5\)

.

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