What does "相兼岂" mean in this sentence from a Taiji Quan manual?
the chopping of the verse is, . . . incorrect lah 
the “體用歌”

太極拳。十三式。妙在二氣分陰陽。化生千億歸抱一。歸抱一。太極拳。兩儀四象渾無邊。禦風何似頂頭懸。我有一轉語。今為知者吐。湧泉無根腰無主。力學垂死終無補。體用相兼豈有他。浩然氣能行乎手。掤捋擠按採捩肘靠。進退顧盼定。不化自化走自走。足欲向前先挫後。身似行雲。打手安用手。渾身是手手非手。但須方寸隨時守所守。

roughly, “體” means “noumenon“ (本體); “用” means “usage” (使用)
so, the verse “體用相兼豈有他” should be interpreted as:
the noumenon (體) &amp; usage (用), both (相) [should be] taken care of (兼 -&gt; 兼顧); there’s no other way (豈有他)
have fun :)