It is a right-angled triangle ABD and there is a small right-angle triangle ABC inside it.
HINT:AB⊥BD,BCD is an straight line, BC=2times(CD),AC=5cm and AD=rooting45
find the area of triangle ACD
(from f.2 mathematics in action chapter 12 page15 question no.14
f.2 math-pythgoras theorem
2012-06-03 5:46 am
回答 (1)
2012-06-03 6:14 am
✔ 最佳答案
let CD be x cm and AB be y cm.then, BC = 2x
AB² = AC² - BC² (pyth. theorem)
y² = (5)² - (2x)² = 25 - 4x² -- (1)
also,
AB² = AD² - BD² (pyth. theorem)
y² = (sqrt45)² - (3x)² = 45 - 9x² (2)
sub (1) into (2)
25-4x²=45-9x²
5x² = 20
x = 2 (since x > 0)
put x=2 into (1), y²=25-4(2²)=9
thus y =3 (since y>0)
area of triangle ACD
= CD*AB /2
= xy/2
= (2)(3)/2
= 3cm²
收錄日期: 2021-04-16 14:27:56
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