Given that ∠B ≅ ∠C.
to prove that the sides AB = AC
This can be done by the method of contradiction.  
If possible let AB  =AC
=AC
Then either AB>AC or AB<AC
Case i:  If AB>AC, then by triangle axiom, Angle C > angle B.
But since angle C = angle B, we get AB cannot be greater than AC
Case ii:  If AB<AC, then by triangle axiom, Angle C < angle B.
But since angle C = angle B, we get AB cannot be less than AC
Conclusion:
Since AB cannot be greater than AC nor less than AC, we have only one possibility. that is AB =AC
Hence if angle B = angle C it follows that 
 AB = AC, and AB ≅ AC.
 
        
                    
             
        
        
        
Answer:
4. 21
5.120
Step-by-step explanation:
(the answer for #4
 I added 5x+15 and 3x-3
and got
8x+12
and because we needed to find the value of x, l did this
8x+12=180
because interior consecutive angles equal 180
and I got 21
(answer for 5)
I then plugged 21 into 5x+15 because angle 1 is equal to it
5(21)+15
I got 120
 
        
             
        
        
        
Set up and solve an equation of ratios.  Comparing shadow lengths, we get 100/6; comparing heights, we get x/8.  Set these two ratios equal to one another and solve the resulting equation for x:
100       x
----- = ------      Then 6x=800, and x = 800 feet^2 over 6 feet.  Your answer 
   6        8
must have the unit of measurement "ft."
        
             
        
        
        
X=30
explanation:
if we are given that the volume is 27,000, we know that x^3 should equal 27,000
so take the cube root of 27,000 and that is 30
        
             
        
        
        
Remember this rhyme:
Hey Diddle Diddle, the medians the middle:
(Answer for your question: Median is 80%)
You add and divide for the Mean: 
( Answer for your question: Mean is 93)
The mode is the one that appears the most:
( Answer for your question: Mode is 87%)
And the range is the difference between.:
( Answer for your question: Range is 54.)
I hope this helps! :)