Class 10 Maths Chapter 6 Triangles Notes & NCERT Solutions

1. Similarity Criteria for Triangles

Two triangles are similar if their corresponding angles are equal and their corresponding sides are proportional. The primary rules are AAA, SSS, and SAS similarity.

2. Basic Proportionality Theorem (BPT / Thales Theorem)

👉 If a line is drawn parallel to one side of a triangle to intersect the other two sides in distinct points, the other two sides are divided in the same ratio.

In $\Delta ABC$, if $DE \parallel BC$, then:
$\frac{AD}{DB} = \frac{AE}{EC}$

✏️ NCERT Solutions Ex 6.2

Q1. In $\Delta ABC$, $DE \parallel BC$. If $AD = 1.5\text{ cm}$, $DB = 3\text{ cm}$, and $AE = 1\text{ cm}$, find $EC$.

Step 1: By BPT, $\frac{AD}{DB} = \frac{AE}{EC}$

Step 2: $\frac{1.5}{3} = \frac{1}{EC} \implies \frac{1}{2} = \frac{1}{EC}$

Step 3: Cross multiply to find $EC = 2\text{ cm}$.

CBSE Class 10 Maths Chapter 6: Triangles Notes

1. Similarity Criteria for Triangles

2. Basic Proportionality Theorem (BPT / Thales Theorem)

✏️ NCERT Solutions Ex 6.2