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$3x+2x^2=90$ $2x^2+3x-90=0$ $2x^2+15x-12x-90=0$ $x(2x+15)-6(2x+15) = 0$ $(2x+15)(x-6)=0$