Question

how to solve this question (19,20,21)​

Answer 1

Answer:

19.

$x = 5 - 3 \sqrt{2}$

$\frac{1}{x} = \frac{1}{5 - 3 \sqrt{2} }$

$rationalising$

$\frac{1}{x } = \frac{1 \times (5 + 3 \sqrt{2)} }{5 - 3 \sqrt{2}(5 + 3 \sqrt{2} ) }$

$\frac{1}{x} = \frac{5 + 3 \sqrt{2} }{25 -18 }$

$\frac{1}{x} = \frac{5 + 3 \sqrt{2} }{7}$

20.

First 5 composite numbers are

$4,6,8,9,10$

Mean =

$\frac{4 + 6 + 8 + 9 + 10}{5}$

$\frac{37}{5} = 7.4$

21.

Adjacent angles of a parallelogram sum up-to 180 degree.

$taking \: angle \: x \\ 7x + 2x = 180 \\ 9x = 180$

$x = 20$

Angles are

$7(20) = 140 \\ 2(20) = 40$

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Answer 2

Answer:

(19) 1/x = (5+3√2) / 7

(20) Mean= 7.4

(21) In parallelogram ABCD,

Angle A = Angle C = 7x = 7×20 ° = 140°

Angle B = Angle D = 2x = 2×20° = 40°

Step-by-step explanation:

(19) Given, x = 5-3√2

so, 1/x = 1/(5-3√2)

[multiplying by conjugate surd]

= 1/(5-3√2) × (5+3√2)/(5+3√2)

= [1× (5+3√2)] / [(5-3√2) × (5+3√2)]

= (5+3√2) / 25-18

= (5+3√2) / 7

(20) first five composite numbers are:

4,6,8,9 and 10

mean = (4+6+8+9+10)/5

_

x = 37/5

_

x = 7.4

(21) let the parallelogram be ABCD in which angles A and B are adjacent angles & angles CD are adjacent angles. Angle A and Angle C are opposite angles & Angle B and Angle D are opposite angles.

so, Angle A : Angle B = 7:2

so, Angle A = 7x , Angle B = 2x

As per the property of parallelogram, opposite angles are equal.

so, Angle A = Angle C = 7x

and Angle B = Angle D = 2x

in parallelogram ABCD ,

Angle A + Angle B + Angle C + Angle D = 360°

7x + 2x + 7x + 2x = 360°

18x = 360°

x = 20°

Hence, Angle A = Angle C = 7x = 7×20 ° = 140°

Angle B = Angle D = 2x = 2×20° = 40°

#BAL

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