SSC CHSL Topic Wise Study Material – Quantitative Aptitude – Surds and Indices
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In this chapter, we deals with questions based on index and surds of a number. Dealing with the topic candidate must have proper knowledge of basic concept and principle of surds and indices.
Surds
Any root of a rational number which cannot be exactly obtained is called a surd, e.g., √2, √6, √8, 3√4 etc.
Order of Surds
Let P be a rational number and m be a positive integer such that P1/m = √P is irrational. Then, m√P is called surds of mth order.
e.g., 7½ = √7 = Surds of 2nd order.
Some Important and Basic Rules of Surds
Method of Arranging Surds in Increasing or Decreasing Order
Suppose given surds are p1/a, q1/b and r1/c
First of all, take the LCM of a, b and c and use it to make the denominator of the powers the same. Then, easily we can find the required order.
Example The greatest among the numbers 3√2, 3√7, 6√5, 2√20 is
(a)3√2
(b)3√7
(c)6√5
(d)2√20
Operations on Surds
Addition and Subtraction
To add or subtract a surd, first make the possible factors of the terms, then add or subtract, i. e., Let x = √80 + 3√245 – √125
√80=√16 x 5=4√5; 3√245 =3√49×5=21√5; √125=√25×5=5√5 ,x=5√5
Example If √18225 = 135, then the value of √18225 + √182.25 + √1.8225 + √0.018225 is SSC (10 + 2) 2012
(a) 1.49985
(b) 14.9985
(c) 149.985
(d) 1499.85
Multiplication and Division
To multiply or divide the surds, we make the denominators of the powers same, then multiply or divide as usual –
i.e., Let x = √5 x 6√6 x 3√4
Indices
When a number ‘P’ is multiplied by itself ‘n’ times then the product is called nth power of ‘P and is written as Pn. Here, P is called the base an ‘n’ is known as the index of the power. (Here, plural of index is called indices)
Some Important and Basic Rules of Indices
Essential Points
Reference Corner
1. If a1/3 + b1/3 + c1/3 = 0, then a relation among a, b, c is SSC (10 + 2) 2014
(a) a + b + c = 3abc
(b) a3 + b3 + c3 = 0
(c) a + b + c=0
(d)(a + b+ c)3 =27abc
Answer:
2. If 3√a + 3√b = 3√c, then the simplest value of (a + b – c)3 + 27abc is ssc (10+2) 2014
(a) -3
(b) 0
(c) -1
(d) 3
Answer:
3. Which one of the following is true? SSC (10+2) 2014
(a) √5 + √3 > √6 +√2
(b) √5 + √3 < √6 +√2
(c) √5 + √3 = √6 +√2
(d)(√5 +√3)( √6 + √2)=1
Answer:
4. Let 3√a = 3√26 + 3√7 + 3√63 . Then, SSC (10+2) 2013
(a) a >729
(b)a = 729
(c) a <729 but a >216
(d)a<216
Answer:
5. The value of (xb+c)b-c (xc+a)c-a (xa+b)a-b
(a)-1
(b)0
(c) 1
(d) 2
Answer:
6. If x = √3 + √2 and y = √3 – √2, then the value of 8xy (x² + y²) is SSC (10 + 2) 2013
(a) 16√6
(b)32
(c) 48√2
(d)80
Answer:
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