Important for :

1

A

∴ | 1 | × h × b = 12 |

2 |

⇒ | 1 | × 3 × b = 12 |

2 |

⇒ b = 8 cm

Here, BD =

CD = | b | = | 8 | = 4 cm |

2 | 2 |

In right-angled ΔABD, by pythagoras theorem,

AB = |
AD^{2} + BD^{2} |

a = |
3^{2} + 4^{2} |
= | 25 | = 5 cm |

Now, perimeter of an isosceles triangle = 2a + b = 2 × 5 + 8 = 18 cm

Hence, option A is correct.

2

3

4

5