Chứng minh:
a) \(\overrightarrow {MN} + \overrightarrow {QE} + \overrightarrow {PQ} + \overrightarrow {NP} = \overrightarrow {ME} \);
b) \(\overrightarrow {AB} + \overrightarrow {MN} + \overrightarrow {BC} + \overrightarrow {CA} + \overrightarrow {PQ} + \overrightarrow {NM} = \overrightarrow {PQ} \);
c) \(\overrightarrow {FK} + \overrightarrow {MQ} - \overrightarrow {FP} - \overrightarrow {MP} + \overrightarrow {QK} = 2\overrightarrow {PK} \);
d) \(\overrightarrow {AD} + \overrightarrow {MP} + \overrightarrow {EK} - \overrightarrow {EP} - \overrightarrow {MD} = \overrightarrow {AK} \).