Exercise Solutions
1. Find the roots of the following quadratic equations by factorisation:
(i) ${x^2 – 3x – 10 = 0}$
Solution:
${x^2 – 3x – 10 = 0}$ => ${x^2 – 5x+ 2x – 10 = 0}$
$x(x-5)+2(x-5)$
$(x-5)(x+2)$
i.e $x=5$ and $-2$
(ii) ${2x^2 + x – 6 = 0}$
Solution:
${2x^2 + x – 6 = 0}$ =>${2x^2 + 4x -3x – 6 = 0}$
${2x(x+2)-3(x+2)}$
$(x+2)(2x-3)$
i.e $x=-2$ and $x=3/2$
(iii) ${ √2x^2 + 7 x + 5 √2 = 0}$
Solution:
${ √2x^2 + 7 x + 5 √2 = 0}$ => ${ √2x^2 + 2 x+ 5x + 5 √2 = 0}$
${√2x(x+√2)+5(x+√2) }$
$(x+√2)(√2x+5)$
i.e $x= - √2 $ or $x= -{5√2}/2$
(iv) ${ 2x^2 – x + 1/8= 0}$
Solution:
(Remember: IN solving fraction type of problem, use multipication method and make it a whole number)
Multiply the equation by 8, therfore
${ 2x^2 – x + 1/8= 0}$ => ${ 16x^2-8x+1}$
$16x^2-4x-4x+1$
$4x(4x-1)-1(4x-1)$
$(4x-1)(4x-1)$
i.e $x=1/4$ or $x=1/4$
(v) ${100 x^2 – 20x + 1 = 0}$
Solution:
${100 x^2 – 20x + 1 = 0}$
$100 x^2 – 10x-10x + 1 = 0$
${10(10x-1)-1(10x-1)}$
$(10x-1)(10x-1)$
i.e $x=1/10$ and $x=1/10$
3. Find two numbers whose sum is 27 and product is 182.
Solution:
Let the number be $x$ and $(27-x)$
Given $x(27-x)=182$
$27x-x^2=182$
$x^2-27x+182$ ( (182= 2× 13 ×7 ))
$x^2-14x -13x+182$
$x(x-14)-13(x-14)$
$(x-14)(x-13)
Ans:The two number are 13 and 14
4. Find two consecutive positive integers, sum of whose squares is 365.
Solution:
Let the two consecutive positive integer be $x$ and $x+1$
Given: $x^2+(x+1)^2 = 365 $
i.e $x^2+x^2+2x+1 = 365$
$2x^2+2x-364=0$
$2x^2+27x-26x-364=0$
$x(2x+27)-13(2x+27)$
$(2x+27)(x-13)$
Since the numbe ris a postive interger, therfore x=13.
Ans: SO, two positive integer are 13 & 14.
5. The altitude of a right triangle is 7 cm less than its base. If the hypotenuse is 13 cm,
find the other two sides.
Solution:
Let the base of the right triangle be $x$ $cm$.
Therefore its altitute = $(x-7)$ $cm$
Therefore , for right triangle,
$H^2=B^2+L^2$
$(13)^2=x^2+(x-7)^2$
$169=x^2 + x^2 -14x+49$
$2x^2-14x-120=0$
$2x^2-24x+10x-120=0$
$2x(x-12)+10(x-12)=0$
$(x-12)(2x+10)$
Therefore base of right triangle $x=12$ $cm$ and its altitute is $5$ $cm$
6. A cottage industry produces a certain number of pottery articles in a day. It was observed
on a particular day that the cost of production of each article (in rupees) was 3 more than
twice the number of articles produced on that day. If the total cost of production on that
day was ₹ 90, find the number of articles produced and the cost of each article.
Solution
Let the number of pottery article produced in a day be $x$
Given: Cost of production of each pottery article in a day = 3+2x
Total cost of production in that particular day = ₹ 90
Therefore $x(3+2x)=90$
i.e$3x+2x^2=90$
$2x^2+3x-90=0$
$2x^2+15x-12x-90=0$
$x(2x+15)-6(2x+15) = 0$
$(2x+15)(x-6)=0$