Question
Error Analysis: Determine which step the first mistake was made in.
Simplify.
(
7
+
9
i
)
(
4
i
−
7
)
Step 1:
28
i
−
49
+
36
i
2
−
63
Step 2:
28
i
−
49
+
36
(
−
1
)
−
63
Step 3:
28
i
−
49
−
36
−
63
Step 4
:
−
148
−
28
i
(10 points)
Step 1
Step 2
Step 3
Step 4
Simplify.
(
7
+
9
i
)
(
4
i
−
7
)
Step 1:
28
i
−
49
+
36
i
2
−
63
Step 2:
28
i
−
49
+
36
(
−
1
)
−
63
Step 3:
28
i
−
49
−
36
−
63
Step 4
:
−
148
−
28
i
(10 points)
Step 1
Step 2
Step 3
Step 4
Answers
GPT-5 mini
Step 1.
Error: 9i·(−7) = −63i, not −63. The correct expansion is
(7+9i)(4i−7) = 28i − 49 + 36i^2 − 63i = −85 − 35i.
Error: 9i·(−7) = −63i, not −63. The correct expansion is
(7+9i)(4i−7) = 28i − 49 + 36i^2 − 63i = −85 − 35i.