pls answer 19 20

Q.19. Two concentric circles are of radii 6.5 cm and 2.5 cm. Find the length of the chord of larger circle which is tangent to smaller circle.

Q.20. Find the area of the shaded region in figure, if BC = BD = 8 cm, AC = AD = 15 cm and O is the centre of the circle. ( Take $\mathrm{\pi }$ = 3.14).

20-      1) find ab using pythagoras theorem  as ANGLE  C=90 degree as ab subtends an angle on the circle
            2)  find area of triangle abc using 1/2*al*base = 1/2 * 15*8
            3)find area of semi circle
            4) subtract area of triangle from area of semicircle=area of shaded region of semi circle
            5) so , area of shaded region=2*area of shaded region of semi circle

you can see the 19^th answer from ncert solutions

  19 . Radius of bigger circle(R) = 6.5cm
       Radius of smaller circle(r) = 2.5cm
       The chord of the bigger circle becomes a tangent to the smaller circle.
        Using Pythagoras Theorem - 
       (6.5)² = (2.5)² + BA²
       42.25 = 6.25 + BA²
       42.25-6.25 = BA²
       36 = BA²
        .:. BA = root of 36
        BA = 6cm
        Length of the chord = 2 x 6
                                         =12cm.

 

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