Convert (r, θ) ↔ (x, y) using x = r cos θ and y = r sin θ — and the reverse for known quadrants. Standards: CCSS HSN-CN.B.4 (move between rectangular and polar coordinates). Each problem matches an answer in the design grid above. As students color in their answers, a symmetrical pattern appears. If the pattern looks right, the work is right — easy for students to catch mistakes and easy for you to spot-check at a glance. Works for classwork, homework, extra practice, extra credit, or sub plans.