Answer:
b = 21.9 cm
Explanation:
Please see attached photo for details.
We'll begin by calculating the length of BC. This can be obtained by using pythagoras theory as illustrated below:
AB = 41 cm
AC = 9 cm
BC =?
AB² = BC² + AC²
41² = BC² + 9²
1681 = BC² + 81
Collect like terms
1681 – 81 = BC²
1600 = BC²
Take the square root of both side
BC = √1600
BC = 40 cm
Next, we shall determine CD.
BC = BD + CD
BD = CD
BC = CD + CD
BC = 2CD
BC = 40 cm
40 = 2CD
Divide both side by 2
CD = 40/2
CD = 20 cm
Finally, we shall determine the value of 'b' this can be obtained as follow:
AC = 9 cm
CD = 20 cm
AD = b cm
AD² = CD² + AC²
b² = 20² + 9²
b² = 400 + 81
b² = 481
Take the square root of both side
b = √481
b = 21.9 cm.