Finding Angle ACB: Triangle with 20° Angle Bisector Problem

Let's remember that an angle bisector divides the angle into 2 equal parts, therefore:

$BAD=DAC=20$

We should also note that we are given:

$ADB=ADC=90$

Since the sum of angles in a triangle is 180, we can determine the size of angle ACB as follows:

Let's focus on triangle ACD, where we know 2 angles and calculate:

$ACB=180-90-20$

$ACB=70$