Triangle Angle Sum Practice: Find the missing angle in each triangle.

To solve the problems in the "Triangle Angle Sum Practice" worksheet, we use the fact that the sum of the interior angles of a triangle is always 180°. Let's go through each problem step by step.

---

Row 1:

#### Problem 1:
- Given angles: \(43^\circ\) and \(90^\circ\) (right angle).
- To find: The missing angle.
- Calculation:
\[
\text{Sum of angles in a triangle} = 180^\circ
\]
\[
? + 43^\circ + 90^\circ = 180^\circ
\]
\[
? = 180^\circ - 43^\circ - 90^\circ = 47^\circ
\]
- Answer: \(47^\circ\)

#### Problem 2:
- Given angles: \(88^\circ\) and \(30^\circ\).
- To find: The missing angle.
- Calculation:
\[
? + 88^\circ + 30^\circ = 180^\circ
\]
\[
? = 180^\circ - 88^\circ - 30^\circ = 62^\circ
\]
- Answer: \(62^\circ\)

#### Problem 3:
- Given angles: \(40^\circ\) and \(98^\circ\).
- To find: The missing angle.
- Calculation:
\[
? + 40^\circ + 98^\circ = 180^\circ
\]
\[
? = 180^\circ - 40^\circ - 98^\circ = 42^\circ
\]
- Answer: \(42^\circ\)

---

Row 2:

#### Problem 4:
- Given angles: \(71^\circ\) and \(40^\circ\).
- To find: The missing angle.
- Calculation:
\[
? + 71^\circ + 40^\circ = 180^\circ
\]
\[
? = 180^\circ - 71^\circ - 40^\circ = 69^\circ
\]
- Answer: \(69^\circ\)

#### Problem 5:
- Given angles: \(50^\circ\) and \(90^\circ\) (right angle).
- To find: The missing angle.
- Calculation:
\[
? + 50^\circ + 90^\circ = 180^\circ
\]
\[
? = 180^\circ - 50^\circ - 90^\circ = 40^\circ
\]
- Answer: \(40^\circ\)

#### Problem 6:
- Given angles: \(40^\circ\) and \(45^\circ\).
- To find: The missing angle.
- Calculation:
\[
? + 40^\circ + 45^\circ = 180^\circ
\]
\[
? = 180^\circ - 40^\circ - 45^\circ = 95^\circ
\]
- Answer: \(95^\circ\)

---

Row 3:

#### Problem 7:
- Given angles: \(30^\circ\) and \(90^\circ\) (right angle).
- To find: The missing angle.
- Calculation:
\[
? + 30^\circ + 90^\circ = 180^\circ
\]
\[
? = 180^\circ - 30^\circ - 90^\circ = 60^\circ
\]
- Answer: \(60^\circ\)

#### Problem 8:
- Given angles: \(51^\circ\) and \(52^\circ\).
- To find: The missing angle.
- Calculation:
\[
? + 51^\circ + 52^\circ = 180^\circ
\]
\[
? = 180^\circ - 51^\circ - 52^\circ = 77^\circ
\]
- Answer: \(77^\circ\)

#### Problem 9:
- Given angles: \(80^\circ\) and \(60^\circ\).
- To find: The missing angle.
- Calculation:
\[
? + 80^\circ + 60^\circ = 180^\circ
\]
\[
? = 180^\circ - 80^\circ - 60^\circ = 40^\circ
\]
- Answer: \(40^\circ\)

---

Final Answers:

\[
\boxed{
\begin{array}{ccc}
47^\circ & 62^\circ & 42^\circ \\
69^\circ & 40^\circ & 95^\circ \\
60^\circ & 77^\circ & 40^\circ
\end{array}
}
\]