SUM AND PRODUCT OF ROOTS OF QUADRATIC EQUATION

If a quadratic equation is given in standard form, we can find the sum and product of the roots using coefficient of x², x and constant term. 

Let us consider the standard form of a quadratic equation,  

ax² + bx + c  =  0

(Here a, b and c are real and rational numbers)

Let α and β be the two zeros of the above quadratic equation. 

Then the formula to get sum and product of the roots of a quadratic equation is,

Example 1 :

Find the sum and product of roots of the quadratic equation given below.

x² - 5x + 6  =  0

Solution :

Comparing

x² - 5x + 6  =  0

and 

ax² + bx + c  =  0

we get

a  =  1, b  =  -5 and c  =  6

Therefore, 

Sum of the roots  =  -b/a  =  -(-5)/1  =  5

Product of the roots  =  c/a  =  6/1  =  6

Example 2 :

Find the sum and product of roots of the quadratic equation given below.

x² - 6  =  0

Solution :

Comparing

x² - 6  =  0

and 

ax² + bx + c  =  0

we get

a  =  1, b  =  0 and c  =  -6

Therefore, 

Sum of the roots  =  -b/a  =  0/1  =  0

Product of the roots  =  c/a  =  -6/1  =  -6

Example 3 :

Find the sum and product of roots of the quadratic equation given below. 

3x² + x + 1  =  0

Solution :

Comparing

3x² + x + 1  =  0

and 

ax² + bx + c  =  0

we get

a  =  3, b  =  1 and c  =  1

Therefore, 

Sum of the roots  =  -b/a  =  -1/3

Product of the roots  =  c/a  =  1/3

Example 4 :

Find the sum and product of roots of the quadratic equation given below.

3x² + 7x  =  2x - 5

Solution :

First write the given quadratic equation in standard form.

3x² +7x  =  2x - 5

3x² + 5x + 5  =  0

Comparing

3x² + 5x + 5  =  0

and 

ax² + bx + c  =  0

we get

a  =  3, b  =  5 and c  =  5

Therefore, 

Sum of the roots  =  -b/a  =  -5/3

Product of the roots  =  c/a  =  5/3

Example 5 :

Find the sum and product of roots of the quadratic equation given below.

3x² -7x + 6  =  6

Solution :

First write the given quadratic equation in standard form.

3x² -7x + 6  =  6

3x² - 7x  =  0

Comparing

3x² - 7x  =  0

and 

ax² + bx + c  =  0

we get

a  =  3, b  =  -7 and c  =  0

Therefore, 

Sum of the roots  =  -b/a  =  -(-7)/3  =  7/3

Product of the roots  =  c/a  =  0/3  =  0

Example 6 :

Find the sum and product of roots of the quadratic equation given below.

x² + 5x + 1  =  3x² + 6

Solution :

First write the given quadratic equation in standard form.

x² + 5x + 1  =  3x² + 6

0  =  2x² - 5x + 5

2x² - 5x + 5  =  0

Comparing

2x² - 5x + 5  =  0

and 

ax² + bx + c  =  0

we get

a  =  2, b  =  -5 and c  =  5

Therefore, 

Sum of the roots  =  -b/a  =  -(-5)/3  =  5/2

Product of the roots  =  c/a  =  5/2

Apart from the stuff given above, if you need any other stuff n math, please use our google custom search here. 

You can also visit the following web pages on different stuff in math. 

WORD PROBLEMS

HCF and LCM  word problems

Word problems on simple equations 

Word problems on linear equations 

Word problems on quadratic equations

Algebra word problems

Word problems on trains

Area and perimeter word problems

Word problems on direct variation and inverse variation 

Word problems on unit price

Word problems on unit rate 

Word problems on comparing rates

Converting customary units word problems 

Converting metric units word problems

Word problems on simple interest

Word problems on compound interest

Word problems on types of angles 

Complementary and supplementary angles word problems

Double facts word problems

Trigonometry word problems

Percentage word problems 

Profit and loss word problems 

Markup and markdown word problems 

Decimal word problems

Word problems on fractions

Word problems on mixed fractrions

One step equation word problems

Linear inequalities word problems

Ratio and proportion word problems

Time and work word problems

Word problems on sets and venn diagrams

Word problems on ages

Pythagorean theorem word problems

Percent of a number word problems

Word problems on constant speed

Word problems on average speed 

Word problems on sum of the angles of a triangle is 180 degree

OTHER TOPICS 

Profit and loss shortcuts

Percentage shortcuts

Times table shortcuts

Time, speed and distance shortcuts

Ratio and proportion shortcuts

Domain and range of rational functions

Domain and range of rational functions with holes

Graphing rational functions

Graphing rational functions with holes

Converting repeating decimals in to fractions

Decimal representation of rational numbers

Finding square root using long division

L.C.M method to solve time and work problems

Translating the word problems in to algebraic expressions

Remainder when 2 power 256 is divided by 17

Remainder when 17 power 23 is divided by 16

Sum of all three digit numbers divisible by 6

Sum of all three digit numbers divisible by 7

Sum of all three digit numbers divisible by 8

Sum of all three digit numbers formed using 1, 3, 4

Sum of all three four digit numbers formed with non zero digits

Sum of all three four digit numbers formed using 0, 1, 2, 3

Sum of all three four digit numbers formed using 1, 2, 5, 6