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# What is the value of (s+t) if the equation

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Manager
Joined: 13 May 2017
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Location: Finland
Concentration: Accounting, Entrepreneurship
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What is the value of (s+t) if the equation  [#permalink]

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23 Nov 2018, 04:14
3
00:00

Difficulty:

25% (medium)

Question Stats:

79% (01:25) correct 21% (01:51) wrong based on 29 sessions

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What is the value of (s+t) if the equation (3$$x^2$$ + tx + s) has 2 and 3 as its roots?

A. 2
B. 3
C. 7
D. 18
E. 33
Senior Manager
Joined: 18 Jun 2018
Posts: 262
Re: What is the value of (s+t) if the equation  [#permalink]

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23 Nov 2018, 06:04
2
OA:B

For the Quadratic equation of form $$ax^2+bx+c=0$$

Sum of roots $$= -\frac{b}{a}$$

Product of roots $$= \frac{c}{a}$$

$$-\frac{t}{3}=2+3=5$$

$$t=-15$$

$$\frac{s}{3}=2*3$$

$$s=18$$

$$s+t = 18+(-15) =3$$
Manager
Joined: 26 Feb 2017
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Location: India
GPA: 3.99
Re: What is the value of (s+t) if the equation  [#permalink]

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23 Nov 2018, 07:02
2
Putting x=2 in the equation 3x^2+tx+s= 0
3(2)^2 + t(2) + s = 0
12 +2t+s = 0
2t + s = -12........eqn 1

Now putting x = 3 in the equation, we get:
27 + 3t + s = 0
3t + s = -27...... eqn 2

Solving eqn 1 & 2, we get:
t = -15
s = 18

Therefore, t + s = -15 + 18 = 3

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Re: What is the value of (s+t) if the equation   [#permalink] 23 Nov 2018, 07:02
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