+0  
 
+1
96
2
avatar+236 

Use completing the square to solve 10r^2 = 45 - 68r.

 Jul 4, 2022
 #1
avatar+124676 
+2

Rewrite as

 

10r^2 + 68r  =  45       divide  through by 10

 

r^2  + (68/10)r  = 45/10

 

r^2 + 6.8r   =  4.5         take 1/2  of  6.8 = 3.4  square it = 11.56  add to both sides

 

{ the number in  red is what we need later }

 

r^2 + 6.8r + 11.56  =  4.5 + 11.56

 

(r + 3.4)^2 =  16.06      take both roots

 

r + 3.4 =   ±√ 16.06

 

r = √16.06  - 3.4  ≈  .6075 

 

or

 

r = - √16.06 - 3.4  ≈ -7.4075

 

 

cool cool cool

 Jul 4, 2022
 #2
avatar+1155 
+10

got this r=(-68-sqrt(6424))/20=-17/5-1/10sqrt(1606)=-7.407

and r=(-68+sqrt(6424))/20=-17/5+1/10sqrt(1606)=0.607

nerdiest  Jul 4, 2022

23 Online Users