sin B=3/5=AC/BC ⇒ AC=3BC/5
AB=BC-7
notam BC=x si aplicam teorema lui Pitagora AB²+AC²=BC²
x²=(x-7)²+(3x/5)²
x²=x²-14x+49+9x²/25
-14x+49+9x²/25=0
-350x+1225+9x²=0
9x²-350x+1225=0
Δ=350²-4×1225×9=784000 √ Δ =√784000=280
x=(350+280)/18=35 deci BC=35cm
AB=35-7=28cm
AC=3×35/5=21cm
Aria=21×28/2=588/2=294 cm²
