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Find all values of t such that 8t^2 \le 3-10t

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 Oct 25, 2014

Best Answer 

 #1
avatar+23254 
+5

Rewrite  8t²  ≤  3 - 10 t  as      8t² + 10t - 3 ≤ 0

Factor:                                (4t - 1)(2t + 3) ≤ 0

Solve the related equality:     (4t - 1)(2t + 3)  =  0 

     If:       4t - 1  =  0     --->     4t  =  1     --->      t  =  1/4  

     If:      2t + 3  =  0     --->     2t  =  -3     --->     t  =  -3/2 

These two points split the number line into three groups:     t ≤ - 3/2     -3/2 ≤ t < 1/4     t ≥ 1/4

Pick any number for t such that   t ≤ - 3/2;  replace it into  8t² + 10t - 3  

     and check to see if that answer ≤ 0:

     I'm going to try -10:        8(-10)² + 10(-10) - 3  =  697;  since this number isn't ≤ 0, these numbers                                                                                               don't work.

Pick any number for t such that  -3/2 ≤ t < 1/4 

     I'm going to try 0:     8(0)² + 10(0) - 3  =  -3; since this aswer is less than zero, these numbers work.

Pick any number for  t  such that     t ≥ 1/4:

     I'm goint to try 1:     8(1)² + 10(1) - 3  =  15; since this answer isn't ≤ 0, these numbers don't work.

Answer:    -3/2  ≤  t <  1/4 

 Oct 26, 2014
 #1
avatar+23254 
+5
Best Answer

Rewrite  8t²  ≤  3 - 10 t  as      8t² + 10t - 3 ≤ 0

Factor:                                (4t - 1)(2t + 3) ≤ 0

Solve the related equality:     (4t - 1)(2t + 3)  =  0 

     If:       4t - 1  =  0     --->     4t  =  1     --->      t  =  1/4  

     If:      2t + 3  =  0     --->     2t  =  -3     --->     t  =  -3/2 

These two points split the number line into three groups:     t ≤ - 3/2     -3/2 ≤ t < 1/4     t ≥ 1/4

Pick any number for t such that   t ≤ - 3/2;  replace it into  8t² + 10t - 3  

     and check to see if that answer ≤ 0:

     I'm going to try -10:        8(-10)² + 10(-10) - 3  =  697;  since this number isn't ≤ 0, these numbers                                                                                               don't work.

Pick any number for t such that  -3/2 ≤ t < 1/4 

     I'm going to try 0:     8(0)² + 10(0) - 3  =  -3; since this aswer is less than zero, these numbers work.

Pick any number for  t  such that     t ≥ 1/4:

     I'm goint to try 1:     8(1)² + 10(1) - 3  =  15; since this answer isn't ≤ 0, these numbers don't work.

Answer:    -3/2  ≤  t <  1/4 

geno3141 Oct 26, 2014

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