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# Solve for x: 3x2 - 21x + 30 = 0?

Topic: Solve for x: 3x2 - 21x + 30 = 0?
June 16, 2019 / By Brittani
Question: someone please explain to me how to solve this the most cleared way u can. so i can get the hang of it and not have a problem solving questions like this anytime

## Best Answers: Solve for x: 3x2 - 21x + 30 = 0?

Alisa | 4 days ago
Factoring, we have.. 3(x² - 7x + 10) = 0 [Factor out the GCF of 3] 3(x - 5)(x - 2) = 0 [Factor the expression] Hence, by zero-product property, we set each factor to 0 and solve for x.. x - 5 = 0 and x - 2 = 0 x = {5, 2} I hope this helps!
👍 216 | 👎 4
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Originally Answered: HOW DO U SOLVE THIS PROBLEM? SOLVE SOLVE "NOT THE ANSWER"?
20 sec. is 20/60 or 1/3 min so you have 8 1/3 min which is 25/3 min. So you'd do the proportion (t = time for light to travel to Jupiter): 25/3 over t = 150 over 779 Cross multiply 150t = 19475/3 so t = 19475/3 ÷ 150 which is 43 5/18 minutes (43 min 16 2/3 sec)

Ulrick
3x² - 21x + 30 = 0 Factor out the common factor of 3 3(x² - 7x + 10) = 0 Find two numbers whose product is 10 and whose sum is -7. Those numbers are -5 and -2. 3(x - 5)(x - 2) = 0 Now find the zeros. x = 5 x = 2 To check the answers, substitute 5 and 2 for x in the original equation. 3(5)² - 21(5) + 30 = 0 3(25) - 105 + 30 = 0 75 - 105 + 30 = 0 75 - 75 = 0 0 = 0 3(2)² - 21(2) + 30 = 0 3(9) - 42 + 30 = 0 27 - 42 + 30 = 0 27 - 27 = 0 0 = 0 Both check out. ANSWER x = 5, 2
👍 90 | 👎 -3

Riordan
Too solve such a quadratic equation follow those steps: 1. The equation is of the form ax^2 - bx + c = 0, determine your a, b and c In our case a= 3, b= -21, and c= 30 2. Figure out your discriminant, which is always equal to b^2 - 4ac In our case (-21)^2 - 4*3*30 = 441 - 360 = 81 3. To find the roots (solutions), follow the formula: x= (-b ± sqrt(Discriminant)) / 2a In our case we get x= (21 ± 9) / 6, that gives as x= 2 or x= 5 There are great algebra video lectures on http://www.khanacademy.org. You should watch this video http://www.khanacademy.org/video/introduction-to-the-quadratic-equation?playlist=Algebra, it will help a lot.
👍 87 | 👎 -10

Meshech
3x^2 - 21x + 30 = 0 Firstly see if you can simplify so your ?x^2 is x^2, hence in this case you would divide it all by 3. 3/3=1 21/3=7 30/3=10 Hence your simplified equation is: x^2 - 7x + 10 = 0 Next is factorising your equation: Think of factors of 10 ---> 10&1 5&2 -10&-1 -5&-2 Then trial them out to see if they will plus/minus to equal -7 (As its a minus number the factors you need will usually be minus numbers) Hence: -10-1=-11 or -5-2=-7 Therefore from this you know your factors will be -5 and -2. So from this you will put the equation into brackets: (x-5)(x-2) Next to solve your equation you need to find the value of x: (x-5) x=5 (x-2) x=2 So your answer is x = 5 x = 2 When you move onto harder equations you may have to use quadratic formula, but for now this is good :) I hope this helps xD
👍 84 | 👎 -17

Originally Answered: Math- I can't figure out how to solve a slope intercept form problem via fraction. Example, help solve?
Use the point-slope form. Given the slope m and a point (x1, y1), the equation of the line is: y - y1 = m(x - x1) So your line is y + 6 = (-4/3)(x + 3) To get it into slope-intercept form, just solve for y. Start by distributing the -4/3: y + 6 = (-4/3)x - 4 y = (-4/3)x - 10

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