Problem Solving: Quadratic Equation


Algebra is one of the main branches of mathematics and is concerned with the study of structure, relation and quantity. Algebra studies the effects of adding and multiplying numbers, variables, and polynomials, along with their factorization and determining their roots. It serves as a pre-requisite for higher-level courses in mathematics like Calculus. Algebra develops one's thinking, specifically logic, patterns, problem solving, and deductive and inductive reasoning.


Algebra is taught in schools by solving basic algebra problems and then moving to a more advanced level course: Algebra 2. This article presents a free algebra problem solver for solving a quadratic equation of the form ax2+bx+c. The solution of equation is derived using three methods: factoring and completing the square and quadratic formula.


Solving the quadratic equation 2x2+17x+21=0



·         Factor 2x2+17x+21

·         Multiply 2 by 21, which is 42.

·         Find factors of 42 which is 2x7x3

·         Ask: Which two numbers add up to 17 and multiply to 42?

·         Answer: 14 and 3

·         Rewrite 17x as the sum of 14x and 3x


·         Factor out common terms in the first two terms, then in the last two terms [2x(x+7)+3(x+7)]=0

·         Factor out the common term x+7


·         The solutions are x=-7 or x=-2/3


Completing the square

·         Dividing the equation 2x2+17x+21 by 2


·         Subtract -21/2 from both sides


·         Complete the square by adding (17/4)2

x2+17/2x+(17/4)2 =-21/2+(17/4)2 => (x+17/4)2=-21/2+289/16   =>(x+17/4)2=121/16

·         Solve for x

x+17/4=±√(121/16)=±11/4 => x=11/4-17/4 or x=-11/4-17/4       =>x=-6/4=-2/3 or x=-28/4=-7

·         The solutions are x=-7 or x=-2/3


Quadratic Formula

The solutions of equation ax2+bx+c where a0 can be found using the quadratic formula x=-b±b2-4ac2a


·         Solve for x for 2x2+17x+21=0

·         Values of a=2, b=17, c=21

·         Solutions of x are

x=-17±√(17)2-4x2x21/2x2 = -17 ±√121/4 = -17± 11/4

·         Either x=-28/4=-7 or x=-6/4=-2/3

The solutions are x=-7 or x=-2/3

Have more questions and cannot figure out the answers? Ask an online Algebra tutor on Acadsoc!

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