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611
2
avatar+422 

Find all numbers such that the square of the number is 84 more than five times the number. If you find more than one, then list all the numbers you find, separated by commas. 

 

I tried guess and check(again). It didnt work out right? Can anyone give me a hint? Like which method?/

 Apr 3, 2020
edited by Guest  Apr 3, 2020

2+0 Answers

 #1
avatar+129852 
+2

x^2  =  5x  + 84      rearrange  as

 

x^2  - 5x  - 84  =  0      factor

 

(x  - 12) ( x + 7)  =   0

 

Set  each factor to  0  and solve  for x  and  we get  that

 

x  = 12    or  x  = -7

 

Check

 

12^2 = 5(12) + 84                 (-7)^2 = 5(-7)  +  84

144  = 60 +  84   OK               49  =  -35  + 84   OK

 

 

cool cool cool

 Apr 3, 2020
 #2
avatar+422 
+2

OHHH Ty Cphill! You come up with clever ways every day!

 Apr 3, 2020

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