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Mathematics

Find the value of x such that :

(i) 23=14x\dfrac{-2}{3} = \dfrac{14}{x}

(ii) 83=x6\dfrac{8}{-3} = \dfrac{x}{6}

(iii) 59=x27\dfrac{5}{9} = \dfrac{x}{-27}

(iv) 116=55x\dfrac{11}{6} = \dfrac{-55}{x}

(v) 15x=3\dfrac{15}{x} = -3

(vi) 36x=2\dfrac{-36}{x} = 2

Rational Numbers

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Answer

(i) 23=14x\dfrac{-2}{3} = \dfrac{14}{x}

We have,

23=14x(2)×x=3×14[cross multiplication]x=3×142x=3×(7)=21\dfrac{-2}{3} = \dfrac{14}{x} \\[1em] \Rightarrow (-2) \times x = 3 \times 14 \quad \text{[cross multiplication]} \\[1em] \Rightarrow x = \dfrac{3 \times 14}{-2} \\[1em] \Rightarrow x = 3 \times (-7) = -21

Hence, x = -21.

(ii) 83=x6\dfrac{8}{-3} = \dfrac{x}{6}

We have,

83=x6(3)×x=8×6[cross multiplication]x=8×63x=8×(2)=16\dfrac{8}{-3} = \dfrac{x}{6} \\[1em] \Rightarrow (-3) \times x = 8 \times 6 \quad \text{[cross multiplication]} \\[1em] \Rightarrow x = \dfrac{8 \times 6}{-3} \\[1em] \Rightarrow x = 8 \times (-2) = -16

Hence, x = -16.

(iii) 59=x27\dfrac{5}{9} = \dfrac{x}{-27}

We have,

59=x279×x=5×(27)[cross multiplication]x=5×(27)9x=5×(3)=15\dfrac{5}{9} = \dfrac{x}{-27} \\[1em] \Rightarrow 9 \times x = 5 \times (-27) \quad \text{[cross multiplication]} \\[1em] \Rightarrow x = \dfrac{5 \times (-27)}{9} \\[1em] \Rightarrow x = 5 \times (-3) = -15

Hence, x = -15.

(iv) 116=55x\dfrac{11}{6} = \dfrac{-55}{x}

We have,

116=55x11×x=6×(55)[cross multiplication]x=6×(55)11x=6×(5)=30\dfrac{11}{6} = \dfrac{-55}{x} \\[1em] \Rightarrow 11 \times x = 6 \times (-55) \quad \text{[cross multiplication]} \\[1em] \Rightarrow x = \dfrac{6 \times (-55)}{11} \\[1em] \Rightarrow x = 6 \times (-5) = -30

Hence, x = -30.

(v) 15x=3\dfrac{15}{x} = -3

Since 3=31-3 = \dfrac{-3}{1}, we have

15x=31(3)×x=15×1[cross multiplication]x=153=5\dfrac{15}{x} = \dfrac{-3}{1} \\[1em] \Rightarrow (-3) \times x = 15 \times 1 \quad \text{[cross multiplication]} \\[1em] \Rightarrow x = \dfrac{15}{-3} = -5

Hence, x = -5.

(vi) 36x=2\dfrac{-36}{x} = 2

Since 2=212 = \dfrac{2}{1}, we have

36x=212×x=(36)×1[cross multiplication]x=362=18\dfrac{-36}{x} = \dfrac{2}{1} \\[1em] \Rightarrow 2 \times x = (-36) \times 1 \quad \text{[cross multiplication]} \\[1em] \Rightarrow x = \dfrac{-36}{2} = -18 \\[1em]

Hence, x = -18.

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